Electroplating process of electroplating an elecrically conductive sustrate

ABSTRACT

An electroplating process of electroplating an electrically conductive substrate is described. The process includes electroplating intermittently to a predetermined plating thickness using the substrate surface as a cathode and a plating metal as an anode at a constant voltage between the anode and the cathode by repeating application of a voltage between a cathode and an anode and interruption of the application alternately. It is described that a voltage time/interruption time ratio is 0.1 to 1.0, a voltage time is not longer than 10 seconds, and an interruption time is not less than 1 x 10 -12  seconds.

This is a Divisional of U.S. pat. application Ser. No. 09/787,139, filedJun. 13, 2001 now U.S. Pat. No. 7,230,188, which entered National Stageon Mar. 14, 2001, and which is a §371 National Stage application ofInternational Application No. PCT/JP99/05003, filed Sep. 14, 1999, thecontents of which are incorporated in their entirety herein byreference.

TECHNICAL FIELD Background Art

With the mounting need for higher functionality and furtherminiaturization of electronic equipment, advances in integrationtechnology of LSI and in size reduction of components, and changes inthe mounting mode, the demand for high-density wiring is getting greaterin the field of printed circuit boards and, as a consequence,development of the so-called multilayer circuit boards comprising 3 ormore conductor layers has been broadly undertaken.

In view of the demand for higher wiring density in multilayer circuitboards, the so-called buildup multilayer circuit board is attractingattention. The buildup multilayer circuit board is manufactured by thetechnology disclosed in Japanese Kokai Publication Hei-4-55555, forinstance. Thus, a core substrate board formed with a lower-layerconductor circuit is coated with an electroless plating adhesivecomprising a photosensitive resin and, after the coat is dried, exposureto light and development are carried out to provide an interlayer resininsulating layer having openings for via holes. Then, the surface ofthis interlayer resin insulating layer is roughened with an oxidizingagent or the like and a thin electroless plated copper layer is formedon said interlayer resin insulating layer. Then, a plating resist isdisposed thereon and a thick electroplated copper layer is constructed.The plating resist is then stripped off and the thin electroless platedcopper layer is etched off to provide a conductor circuit patternincluding via holes. This procedure is repeated a plurality of times toprovide a multilayer printed circuit board.

When, in the above process for fabricating a printed circuit board, thedirect-current plating (DC plating) method, which is one of theconventional electroplating techniques, is used to provide saidelectroplated copper layer on a substrate surface, the current generallytends to be concentrated in the marginal area of the substrate surfaceas compared with the central area so that, as illustrated in FIG. 6, thethickness t₁₂ of the copper layer in the marginal area of the substratesurface tends to become greater than the thickness t₁₁ in the centralarea, thus causing a regional variation in thickness of theelectroplated copper layer.

Since, in actual production runs, said substrate surface is the surfaceof a substrate board (work size substrate) having a large areacorresponding to a large number of printed circuit boards integrated(specifically, the average one has an area of 255 to 510 mm square andthere is even one having an area of about 1020 mm square at a maximum),the above tendency is particularly pronounced.

In the manufacture of printed circuit boards, when the electroplatedcopper layer constituting a conductor circuit is not uniform inthickness, the insulation interval t₁₄ between conductor layers in themarginal region of the substrate board is relatively smaller than theinsulation interval t₁₃ between conductor layers in the central regionof the substrate board as shown in FIG. 7, so that the thickness of theinsulating layer 1101 b between conductor layers must be increased inorder to insure a sufficient insulation in all regions of the printedcircuit board but this is a hindrance to the implementation ofhigh-density wiring.

In addition, when the copper layer is formed by direct current plating,the crystallinity of the plated copper is low because of the use of anorganic additive for improved throwing power. Moreover, the residualstress in the plated copper layer is fairly large so that the layertends to develop cracks and other flaws and show low elongation and hightensile strength characteristics. Therefore, an annealing step forreducing the residual stress has been essential to the manufacture ofprinted circuit boards.

As a technology for insuring the uniformity of thickness of the platedcopper layer, it has been proposed to form a thick plated copper layerby electroless plating alone without electroplating. However, the thickplated copper layer formed by electroless plating is poor in ductilitybecause of the unavoidable contamination of the layer with manyimpurities inclusive of the additives used. Therefore, when a thickplated copper layer is formed by electroless plating, the reliabilityfor the wiring and connection is insufficient and in order to attain asufficient degree of reliability, an annealing step is indispensable inthis case, too.

To overcome the above problem, a technology for constructing a thickplated copper layer by a constant-current pulse electrolytic techniquehas been proposed.

The constant-current pulse electroplating process is characterized inthat the plating current is controlled at a constant level and therepresentative waveform involved is a square wave.

This technology may be further divided into the process (PC platingprocess; FIG. 8) in which the current is controlled by means of thesquare pulse wave available by repetition of the alternating supply (ON)and interruption (OFF) of the cathode current and the pulse-reverseelectroplating method (PR plating method; FIG. 9) in which the currentis controlled with a periodically reversed wave available by repetitionof the alternating supply of cathode current and supply of anodecurrent. As compared with the direct current electroplating process, thenon-steady diffusion layer can be reduced in thickness in eitherprocess, with the result that a smooth plated metal layer can beconstructed and further that since plating can be effected at a highpulse current density (high overvoltage), the evolution of crystal seedsis promoted to yield finer crystal grains, thus enabling formation of aplated metal layer of high crystallinity. As an example of the PRelectroplating method, the process disclosed by Fujinami et al. (SurfaceTechnology, “Formation of Via Filling by PR Electrolysis”, 48 [6], 1997,p.86-87).

However, when the plated copper layer is formed by PC process, theuniformity of layer thickness is superior to that obtainable by directcurrent plating process but is not as good as the objective level (FIG.4).

On the other hand, the plated copper layer formed by PR process isimproved in the uniformity of thickness as compared with the layerobtainable by PC process but is not as high as desired yet and,moreover, plating by PR process requires an expensive current source.

The current mainstream of electroless plating in the manufacture ofprinted circuit boards uses EDTA as a complexing agent, and examples offormation of copper circuits with such electroless plating solutions canbe found in the Best Mode sections of Japanese Kokai PublicationSho-63-158156 and Japanese Kokai Publication Hei-2-188992 (correspondingto U.S. Pat. No. 5,055,321 and U.S. Pat. No. 5,519,177).

However, with a plating solution containing EDTA as a complexing agent,a compressive stress (an expanding force) is generated in the platingmetal layer to cause peeling of the plated copper film from the resininsulating layer.

Furthermore, there is also found the problem not to deposit within finevia holes not over 80 μm in diameter.

Moreover, in the conventional processes for manufacture of printedcircuit boards, it was impossible to construct fine-definition lineconductor circuits on core boards. Thus, the prior art method forforming a conductor circuit on the core substrate board for a printedcircuit board is now described with reference to FIG. 27. As the coresubstrate board, a copper-clad laminate 3330A comprising a resinsubstrate 3330 and, as clad to both sides thereof, a copper foil 3331(FIG. 27 (A)) is used. First, through holes 3332 are drilled in thiscore board (FIG. 27 (B)). Then, a plating metal is uniformly deposited(3333) to form plated-through holes 3336 in said holes 3332 (FIG. 27(C)) . Then, the copper foil 3331 formed with the plated metal layer3333 is subjected to pattern-etching to provide a conductor circuit 3334(FIG. 27 (D)) . After an interlayer resin insulating layer 3350 isformed over said conductor circuit 3134, plating is performed to providea conductor circuit 3358 (FIG. 27 (E)).

In the above process according to the conventional technology, thethickness of copper foil 3331 is at least 18 μm and the thickness of theplated metal layer formed thereon is 15 μm. Since the combined thicknessis as large as 33 μm, etching produces undercuts on the lateral sides ofthe conductor 3334 as shown in FIG. 27 (D) and since the circuit layerthen is liable to peel off, it has been impossible to construct afine-line conductor circuit.

Furthermore, the conductor circuit 3358 on the interlayer resininsulating layer 3350, shown in FIG. 27 (E), has been formed in athickness of about 15 μm. In contrast, the conductor circuit 3334 on thecore board 3330 has a thickness of 33 μm. This means that a largeimpedance difference is inevitable between the conductor circuit 3358 onthe interlayer resin insulating layer 3350 and the conductor circuit3334 on the core board and because of difficulties in impedancealignment, the high-frequency characteristic of the circuit board cannotbe improved.

Moreover, in the above process for fabricating a printed circuit board,when the substrate surface is copper-plated by direct-current (DC)electroplating which is general electroplating technique, the platingmetal is deposited in the same thickness over the via hole openings andthe conductor circuit-forming area.

This results in formation of depressions in the areas of the interlayerresin insulating layer which correspond to the via holes. Anotherproblem is that the structure called “stacked via”, namely formation ofa via hole over a via hole, cannot be constructed.

In addition, for the following reasons, the conventional printed circuitboard has the drawback that its size and thickness are increased beyondwhat are required. Thus, as shown in FIG. 38 (A), the printed circuitboard 5210 for use as a package board for mounting the IC chip 5290 isfabricated by building up interlayer resin insulating layers 5250, 5350and conductor layers 5258, 5358 in an alternating manner on a core board5230 formed with plated-through holes 5236 and disposing bumps 5276U forconnection to the IC chip 5290 on the top surface and bumps 5276D forconnection to a mother board on the bottom side. The electricalconnection between the top and bottom conductor layers is afforded byvia holes 5260, 5360. While the via holes 5260 are adjacent to the ICchip 5290 of the core board 5230, the via holes 5360 adjacent to themother board. These via holes are connected to each other through thecorresponding plated-through holes 5236. Thus, on the face side of thecore board 5230 of this printed circuit board 5210, as shown in FIG. 38(B) which is a sectional view taken along the line B-B of FIG. 38 (A),the land 5236 a of the plated-through hole 5236 is provided with aninner layer pad 5236 b for via-hole connection to the upper layer, whilethe via hole 5260 is connected to this inner layer pad 5236 b.

However, with the prior art land configuration illustrated in FIG. 38(B), the interval between plated-through holes must be large enough toinsure a mutual insulation of inner layer pads 5236 b, thus restrictingthe number of plated-through holes that can be constructed in the coreboard.

On the other hand, the package board is formed with a larger number ofbumps on the face side than on the reverse side. This is because thewirings from the plurality of bumps on the surface are consolidated andconnected to the bumps on the reverse side. For example, the power linesrequired to be of low resistance compared with signal lines, whichnumber 20, for instance, on the face side (IC chip side) areconsolidated into a single line on the reverse side (on mother boardside).

Here, it is preferable that the buildup circuit layer formed on the faceside of a core board and the buildup circuit layer on the reverse sidemay be consolidated at the same pace for the purpose of equalizing thenumber of upper buildup circuit layers to the number of lower buildupcircuit layers, that is to say for minimizing the number of layers.However, as mentioned above, there is a physical restriction to thenumber of plated-through holes which can be formed in a multilayer coreboard. Therefore, in the prior art package board, the wirings areconsolidated to some extent in the buildup circuit layer on the faceside and then connected to the buildup circuit layer on the reverse sidethrough the plated-through holes in the multilayer core board. Since thewiring density has thus been decreased in the buildup circuit layer onthe reverse side, it is intrinsically unnecessary to provide the samenumber of layers on the reverse side as in the buildup circuit layers onthe face side. However, the same number of layers has heretofore beenused because if there is a difference in the number of layers betweenthe face and reverse sides, warping due to asymmetry would beinevitable. Thus, because of said restriction to the number ofplated-through holes which can be provided in the multilayer core board,it is not only necessary to increase the number of layers for thebuildup wiring layer on the face side but also necessary to form thebuildup circuit layer on the reverse side using the same increasednumber of layers on the face side.

Thus, in the prior art multilayered buildup circuit board (packageboard), the number of built-up layers is increased so that thereliability of connection between the upper and lower layers is low.Moreover, the cost of the package board is increased and the size,thickness and weight of the package board are unnecessarily increased.

Furthermore, even when the buildup multilayer circuit board is providedonly on one side of a core board, provision must be made for a freedomin wiring design for the side opposite to the side formed with thebuildup layer.

Moreover, since the connection between plated-through hole 5236 and viahole 5260 is afforded through an inner layer pad 5236 b as describedabove, the wiring length within the printed circuit board is increasedto sacrifice the signal transmission speed, thus making it difficult tomeet the demand for speed-up of IC chips.

SUMMARY OF THE INVENTION

Developed in the above state of the art, the present invention has forits object to provide an electroplating process which, by utilizing aconstant-voltage pulse process is capable of providing with lowequipment cost, an electroplated metal of good crystallinity and uniformdeposition on substrate.

It is another object of the present invention to provide an electrolessplating solution contributory to reduced plating stresses and consequentprotection of the plated metal film against peeling from the innerinsulating layer and capable of forming a plated metal film even in finevia holes and an electroless plating process using said platingsolution.

It is still another object of the present invention to provide a processfor manufacturing a multilayer printed circuit board having an improvedhigh-frequency characteristic.

The present invention has for its additional object to provide a processfor manufacturing multilayer printed circuit boards which is capable ofsimultaneous via hole filling and formation of conductor circuit byelectroplating without using an expensive equipment.

It is a further object of the present invention to provide a multilayerprinted circuit board contributory to reduction in the number of layersof the buildup structure and a multilayer printed circuit boardcontributory to reduction in the internal wiring length.

It is a still further object of the present invention to provide amultilayer buildup circuit board contributory to reduction in theinternal wiring length.

The first invention among inventions belonging to the first group isconcerned with an electroplating process comprising electroplating anelectrically conductive substrate wherein the electroplating isperformed intermittently using said substrate surface as cathode and aplating metal film as anode at constant voltage between said anode andsaid cathode.

The second invention among said inventions belonging to the first groupis concerned with a process for producing a circuit board comprising asubstrate and, as formed thereon, a conductor circuit by electroplatingwherein the electroplating is performed intermittently using theelectrically conductive conductor circuit-forming surface as cathode anda plating metal as anode at a constant voltage between said anode andsaid cathode.

The third invention among said inventions belonging to the first groupis concerned with a process for manufacturing a printed circuit boardwhich comprises disposing a resist on electrically conductive layerformed on a substrate, performing electroplating, stripping the resistoff and etching said electrically conductive layer to provide aconductor circuit, wherein the electroplating is performedintermittently using said electrically conductive layer as cathode and aplating metal as cathode at a constant voltage between said anode andsaid cathode.

The fourth invention among said inventions belonging to the first groupis concerned with a process for manufacturing a printed circuit boardwhich comprises disposing an interlayer resin insulating layer on asubstrate formed with a conductor circuit, creating openings forformation of via holes in said interlayer resin insulating layer,forming an electroless plated metal layer on said interlayer resininsulating layer, disposing a resist thereon, performing electroplating,stripping the resist off and etching the electroless plated metal layerto provide a conductor circuit and via holes, wherein the electroplatingis performed intermittently using said electroless plated metal layer ascathode and a plating metal as anode at a constant voltage between saidanode and said cathode.

The fifth invention among said inventions belonging to the first groupis concerned with a circuit board comprising a substrate and, as builtthereon, a circuit comprised of a copper film which has properties that(a) its crystallinity is such that the X-ray diffraction half-width ofthe (331) plane of copper is less than 0.3 deg and (b) the variation inthickness ((maximum thickness-minimum thickness)/average thickness)) ofthe electroplated copper layer (electroplated metal layer) as measuredover the whole surface of said substrate is not greater than 0.4.

The sixth invention among said inventions belonging to the first groupis concerned with a printed circuit board comprising a substrate and, asbuilt thereon, a circuit comprised of a plated copper film wherein saidplated copper film has properties that (a) its crystallinity is suchthat the X-ray diffraction half-width of (331) plane of copper is lessthan 0.3 deg and (b) the variation in thickness ((maximumthickness-minimum thickness)/average thickness) of said plated copperlayer as measured over the whole surface of said substrate is notgreater than 0.4.

The seventh invention among said inventions belonging to the first groupis concerned with a printed circuit board comprising a substrate formedwith a conductor circuit, an interlayer resin insulating layer builtthereon and a conductor circuit comprised of a copper film as built onsaid interlayer resin insulating layer, said interlayer resin insulatinglayer having vial holes by which said conductor circuits areinterconnected, wherein said copper film has properties that (a) itscrystallinity is such that the X-ray diffraction half-width of (331)plane of copper is less than 0.3 deg and (b) the variation in thickness((maximum thickness-minimum thickness)/average thickness) of said platedcopper layer as measured over the whole surface of said substrate is notgreater than 0.4.

As a prior art technology for constructing a conductor circuit by apulse electroplating method, there is known the PR electrolytic processmentioned hereinbefore but this prior art technology is a plating methodusing a constant current and not a constant-voltage pulse electroplatingprocess wherein the voltage is controlled.

The first invention among inventions belonging to a second group isconcerned with an electroless plating solution comprising an aqueoussolution containing 0.025 to 0.25 mol/L of a basic compound, 0.03 to0.15 mol/L of a reducing agent, 0.02 to 0.06 mol/L of copper ion and0.05 to 0.30 mol/L of tartaric acid or a salt thereof.

The second invention among said inventions belonging to the second groupis concerned with an electroless plating solution comprising an aqueoussolution containing a basic compound, a reducing agent, copper ion,tartaric acid or a salt thereof and at least one ion species selectedfrom the group consisting of nickel ion, cobalt ion and iron ion.

The third invention among said inventions belonging to the second groupis concerned with an electroless plating process which comprisesimmersing a substrate in the electroless plating solution according toeither said first invention or said second invention and performingelectroless copper plating at a deposition rate set to 1 to 2 μm/hour.

The fourth invention among said inventions belonging to the second groupis concerned with a process for manufacturing a printed circuit boardwhich comprises immersing a resin insulating substrate board in theelectroless plating solution according to either said first invention orsaid second invention and performing electroless copper plating at adeposition rate set to 1 to 2 μm/hour to provide a conductor circuit.

The fifth invention among said inventions belonging to the second groupis concerned with a printed circuit board comprising a resin insulatingsubstrate board formed with a roughened surface and, as built thereon, aconductor circuit comprising at least an electroless plated film whereinthat said electroless plated film has a stress of 0 to +10 kg/mm².

The sixth invention among said inventions belonging to the second groupis concerned with a printed circuit board comprising a resin insulatingsubstrate board formed with a roughened surface and, as built thereon, aconductor circuit comprising at least an electroless plated film whereinsaid electroless plated film is complementary to said roughened surfaceand convex areas of the roughened surface is relatively greater inthickness than said film in concave areas of said roughened surface.

The seventh invention among said inventions belonging to the secondgroup is concerned with a printed circuit board comprising a substrateboard formed with a lower-layer conductor circuit and, as built thereon,an upper-layer conductor circuit through the intermediary of aninterlayer resin insulating layer, with said upper-layer conductorcircuit and said lower-layer conductor circuit being interconnected byvia holes,

wherein said upper-layer conductor circuit comprises at least anelectroless plated film, said interlayer resin insulating layer isprovided with a roughened surface, said electroless plated film iscomplementary to said roughened surface, and bottoms of said via holesare also provided with an electroless plated film having a thicknessequal to 50 to 100% of the thickness of the electroless plated film onsaid interlayer resin insulating layer.

The eighth invention among said inventions belonging to the second groupis concerned with a printed circuit board comprising a resin insulatingsubstrate board and, as built thereon, a conductor circuit comprising atleast an electroless plated film, wherein said electroless plated filmcomprises copper and at least one metal species selected from the groupconsisting of nickel, iron and cobalt.

The first invention among inventions belonging to a third group isconcerned with a process for manufacturing a multilayer printed circuitboard comprising at least the following steps (1) to (5).

-   (1) a step for thinning the copper foil of a copper-clad laminate by    etching-   (2) a step for piercing through holes in said copper-clad laminate-   (3) a step for depositing a plated metal film on said copper-clad    laminate to construct plated-through holes within said through holes-   (4) a step for pattern-etching the copper foil and plated metal film    on said copper-clad laminate to construct a conductor circuit-   (5) a step for serially building up an interlayer resin insulating    layer and a conductor layer alternately over said conductor circuit.

The second invention among said inventions belonging to the third groupis concerned with a process for manufacturing a multilayer printedcircuit board comprising at least the following steps (1) to (7):

-   (1) a step for thinning the copper foil of a copper-clad laminate by    etching-   (2) a step for piercing through holes in said copper-clad laminate-   (3) a step for forming a conductor film on said copper-clad laminate-   (4) a step of disposing a resist on areas free from conductor    circuits and plated-through holes-   (5) a step for providing a plated metal film in the resist-free area    to construct a conductor circuit and plated-through holes-   (6) a step for stripping off said resist and etching the conductor    film and copper foil under the resist-   (7) a step for serially building up an interlayer resin insulating    layer and a conductor layer alternately over said conductor circuit.

The third invention among inventions belonging to the third group isconcerned with a multilayer printed circuit board which comprises a coreboard having a conductor circuit and, as built over said conductorcircuit, a buildup wiring layers comprising obtainable by building up aninterlayer resin insulating layer and a conductor layer alternately withthe conductor layers being interconnected by via holes, wherein thethickness of the conductor circuit on said core board is not greater bymore than 10 μm than the thickness of the conductor layer on saidinterlayer resin insulating layer.

The fourth invention among said inventions belonging to the third groupis concerned with a process for manufacturing a multilayer printedcircuit board which comprises thinning the copper foil of a copper-cladlaminate by etching, pattern -etching the copper foil of saidcopper-clad laminate to construct a conductor circuit and building upserially an interlayer resin insulating layer and a conductor layeralternately over said conductor circuit wherein the thickness of theconductor circuit on said core board is controlled so as to be notgreater by more than 10 μm than the thickness of the conductor layer onsaid interlayer resin insulating layer.

The invention belonging to a fourth group is concerned with a processfor manufacturing a multilayer printed circuit board which comprisesconstructing an interlayer insulating layer on a substrate formed with alower-layer conductor circuit, piercing openings in said interlayerinsulating layer, imparting electrical conductivity to the surface ofsaid interlayer insulating layer and the inner walls of said openings,performing electroplating to fill up said openings and thereby providevia holes and, at the same time, construct an upper-layer conductorcircuit, wherein said electroplating is performed using an aqueoussolution containing a metal ion and 0.1 to 1.5 mmol/L of at least oneadditive selected from the group consisting of thioureas, cyanides andpolyalkylene oxides as a plating solution.

The first invention belonging to a fifth group is concerned with amultilayer printed circuit board comprising a core board havingplated-through holes and, as constructed on both sides thereof, abuildup wiring layers obtainable by building up an interlayer resininsulating layer and a conductor layer alternately with said conductorlayers being interconnected by via holes, wherein said via holes areformed in the manner of plugging the holes in plated-through holes insaid core board.

The second invention belonging to the fifth group is concerned with aprocess for manufacturing a multilayer printed circuit board comprisingat least the following steps (1) to (4):

-   (1) a step for piercing through holes not larger than 200 μm in    diameter in a core board by laser-   (2) a step for plating said through holes to construct    plated-through holes therein-   (3) a step for constructing an interlayer resin insulating layer    provided with openings communicating with said plated-through holes    on the core board-   (4) a step for plating the openings in said interlayer resin    insulating layer to construct via holes in the manner of plugging    the holes in said plated-through holes.

The first invention among inventions belonging to a sixth group isconcerned with a multilayer printed circuit board comprising a coreboard and, as constructed on both sides thereof, a buildup wiring layersobtainable by building up an interlayer resin insulating layer and aconductor layer alternately with via holes interconnecting conductorlayers, wherein the via holes in a lower layer are disposed immediatelyover the plated-through holes formed in said core board and via holes inan upper layer are disposed immediately over said via holes in the lowerlayer.

The second invention among said inventions belonging to the sixth groupis concerned with a multilayer printed circuit board comprising a coreboard having plated-through holes and, as constructed on both sidesthereof, a buildup wiring layers obtainable by building up an interlayerresin insulating layer and a conductor layer alternately with via holesinterconnecting conductor layers, wherein said plated-through holes ofcore board are filled with a filler, with the surfaces of said fillerwhich are exposed from said plated-through holes being covered with aconductor layer provided with lower-layer via holes, with upper-layervia holes being disposed immediately over said lower-layer via holes.

The third invention among said inventions belonging to the sixth groupis concerned with a multilayer printed circuit board comprising a coreboard and, as constructed on both sides thereof, a buildup wiring layersobtainable by building up an interlayer resin insulating layer and aconductor layer alternately with via holes interconnecting conductorlayers wherein the via holes in a lower layer are disposed to plug theholes in plated-through holes of said core board, with via holes in anupper layer being disposed immediately over said via holes in the lowerlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (a) to (g) are diagrams illustrating the conductorcircuit-fabricating step in the processes for manufacture of printedcircuit boards which belong to a first group of the present invention.

FIG. 2 (a) to (e) are diagrams illustrating the printed circuitboard-fabricating step in the processes for manufacture of printedcircuit boards which belong to the first group of the present invention.

FIG. 3 (a) to (b) are diagrams showing exemplary current and voltagewaveforms for the constant-voltage pulse plating process.

FIG. 4 is a diagram showing the results of evaluation of the depositionuniformity of the electroplated copper layers constructed by four kindsof electroplating techniques, namely the direct-current platingtechnique, PC plating technique, PR plating technique andconstant-voltage pulse plating technique.

FIG. 5 is a diagram showing the result of X-ray diffraction analysis ofthe electroplated copper layer formed by the constant-voltage pulseplating technique.

FIG. 6 is a schematic diagram illustrating the electroplated copperlayer formed on an insulating board by the conventional direct-currentelectrolytic technique.

FIG. 7 is a schematic diagram illustrating the disadvantage encounteredin laminating the printed circuit board prepared by the techniqueaccording to FIG. 6.

FIG. 8 (a) to (b) are diagrams showing exemplary current and voltagewaveforms for the PC plating technique.

FIG. 9 (a) to (b) are diagrams showing exemplary current and voltagewaveforms for the PR plating technique.

FIG. 10 (a) to (d) are views illustrating the production flow for themanufacture of a CMOS IC.

FIG. 11 (a) to (d) are sectional views showing a part of the process formanufacture of printed circuit boards according to a second group of thepresent invention.

FIG. 12 (a) to (d) are sectional views showing a part of the process formanufacture of printed circuit boards according to the second group ofthe present invention.

FIG. 13 (a) to (d) are sectional views showing a part of the process formanufacture of printed circuit boards according to the second group ofthe present invention.

FIG. 14 (a) to (c) are sectional views showing a part of the process formanufacture of printed circuit boards according to the second group ofthe present invention.

FIG. 15 (a) to (c) are sectional views showing a part of the process formanufacture of printed circuit boards according to the second group ofthe present invention.

FIG. 16 is a partially exaggerated schematic sectional view showing thethickness profile of the electroless plated metal layer formed by theprocess according to the second group of the present invention.

FIG. 17 (A) to (E) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 18 (F) to (I) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 19 (J) to (M) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 20 (N) to (P) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 21 (Q) to (S) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 22 (T) to (U) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 23 is a cross-section view showing a multi-layer printed circuitboard according to this invention.

FIG. 24 (A) to (F) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 25 (A) to (E) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 26 (A) to (E) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the thirdgroup of the present invention.

FIG. 27 (A) to (E) are cross-section views showing a part of theconventional process for manufacture of multilayer printed circuitboards.

FIG. 28 (a) to (d) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the fourthgroup of the present invention.

FIG. 29 (a) to (d) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the fourthgroup of the present invention.

FIG. 30 (a) to (d) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the fourthgroup of the present invention.

FIG. 31 (a) to (c) are sectional views showing a part of the process formanufacture of multilayer printed circuit boards according to the fourthgroup of the present invention.

FIG. 32 (A) to (E) are cross-section views illustrating a part of theproduction process for multilayer printed circuit boards according to afifth group of the present invention.

FIG. 33 (F) to (I) are cross-section view showing a part of theproduction process for the multilayer printed circuit board according toa fifth group of the present invention.

FIG. 34 (J) to (M) are cross-section view showing a part of theproduction process for the multilayer printed circuit board according tothe fifth group of the present invention.

FIG. 35 (N) to (Q) are cross-section views showing a part of theproduction process for the multi-layer printed circuit board inaccordance with the fifth group of the present invention.

FIG. 36 (R) is a cross-section view of the multi-layer printed circuitboard according to the fifth group of the present invention and FIG. 36(S) is a sectional view taken along the line S-S of FIG. 36 (R).

FIG. 37 is a cross-section view of the multi-layer printed circuit boardaccording to the fifth group of the present invention.

FIG. 38 (A) is a cross-section view of the conventional multi-layerprinted circuit board and FIG. 38 (B) is a sectional view taken alongthe line B-B of FIG. 38 (A).

FIG. 39 (A) to (E) are cross-section views illustrating a part of theproduction process for multilayer printed circuit boards according tothe sixth group of the present invention.

FIG. 40 (F) to (J) are cross-section view showing a part of theproduction process for the multilayer printed circuit board according tothe sixth group of the present invention.

FIG. 41 (K) to (O) are cross-section view showing a part of theproduction process for the multilayer printed circuit board according tothe sixth group of the present invention.

FIG. 42 (P) to (T) are cross-section views showing a part of theproduction process for the multi-layer printed circuit board accordingto the sixth group of the present invention.

FIG. 43 (U) to (X) are cross-section views showing a part of theproduction process for the multi-layer printed circuit board accordingto the sixth group of the present invention.

FIG. 44 is a cross-section view showing a multi-layer printed circuitboard according to the sixth group of the present invention.

FIG. 45 is a cross-section view showing a multi-layer printed circuitboard according to the sixth group of the present invention.

FIG. 46 is a cross-section view showing a multi-layer printed circuitboard according to the sixth group of the present invention.

FIG. 47 (A) illustrates a structure of the multi-layer printed circuitboard according to the sixth group of the present invention and FIG. 47(B) illustrates a structure of the multi-layer printed circuit boardaccording to the sixth group of the present invention.

FIG. 48 illustrates an example of a structure of the multi-layer printedcircuit board according to the sixth group of the present invention.

FIG. 49 is a cross-section view showing a multi-layer printed circuitboard according to the sixth group of the present invention.

FIG. 50 is a cross-section view showing a multi-layer printed circuitboard according to the sixth group of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is now described in detail. Unless otherwiseindicated, the thickness of any copper foil, conductor layer orconductor circuit as mentioned in this specification is the mean ofthicknesses measured on a light or electron microphotograph of itscross-section.

The first invention among the inventions belonging to the first group isconcerned with an electroplating process for electroplating a conductivesubstrate surface wherein said electroplating is performedintermittently using said substrate surface as cathode and a platingmetal as anode at a constant voltage between said anode and saidcathode.

The intermittent electroplating in the above electroplating process iscarried out by repeating application of a voltage between the cathodeand anode and interruption thereof in an alternating pattern, andpreferably the voltage time/interruption time ratio is 0.01 to 100, thevoltage time is not longer than 10 seconds and the interruption time isnot shorter than 1×10⁻² seconds.

The second invention among the inventions belonging to the first groupis concerned with a process for producing a circuit board whichcomprises forming a conductor circuit on a substrate board byelectroplating,

wherein said electroplating is performed intermittently using theconductive surface on which a conductor circuit is to be formed ascathode and a plating metal as anode at a constant voltage between saidanode and said cathode.

In the above process for producing a circuit board, said intermittentelectroplating is carried out by repeating application of a voltagebetween the cathode and anode and interruption thereof in an alternatingpattern, and preferably the voltage time/interruption time ratio is 0.01to 100, the voltage time is not longer than 10 seconds and theinterruption time is not shorter than 1×10⁻² seconds.

It should be understood that the above circuit comprises electrodes andmounting pads in addition to a conductor circuit pattern.

The third invention among the inventions belonging to the first group isconcerned with a process for producing a printed circuit board whichcomprises disposing a resist on a conductive layer on a substrate board,performing electroplating, stripping the resist off, and etching saidconductive layer to provide a conductor circuit,

wherein said electroplating is performed intermittently using saidconductive layer as cathode and a plating metal as anode at a constantvoltage between said anode and said cathode.

The fourth invention among the inventions belonging to the first groupis concerned with a process for producing a printed circuit board whichcomprises constructing an interlayer resin insulating layer on aconductor circuit-forming substrate board, forming openings for viaholes in said interlayer resin insulating layer, forming an electrolessplated metal layer over said interlayer resin insulating layer,disposing a resist thereon, performing electroplating, stripping theresist off and etching the electroless plated metal layer to form aconductor circuit pattern and via holes, wherein said electroplating isperformed intermittently using said electroless plated metal layer ascathode and a plating metal as anode at a constant voltage between saidanode and said cathode.

In the above process for producing a printed circuit board, a metallayer may have been formed on the surface of the interlayer resininsulating layer.

The intermittent electroplating in the above third and fourth inventionscomprises application of a voltage between the cathode and anode andinterruption thereof in an alternating pattern, and preferably thevoltage time/interruption time ratio is 0.01 to 100, the voltage time isnot longer than 10 seconds and the interruption time is not shorter than1×10⁻² seconds.

The fifth invention among the inventions belonging to the first group isconcerned with a circuit board having a copper film circuit on asubstrate board, wherein said copper film has properties (a) itscrystallinity is such that the half-width of X-ray diffraction of the(331) plane of copper is less than 0.3 deg. and (b) the variation inthickness of said copper film (electroplated copper layer) measured overthe whole surface of said substrate, i.e. ((maximum thickness-minimumthickness)/average thickness), is not greater than 0.4.

In the circuit board mentioned above, the percent elongation of saidcopper film as a characteristic parameter is preferably not less than7%.

The sixth invention among the inventions belonging to the first group isconcerned with a printed circuit board comprising a copper film circuiton a substrate board, wherein said copper film has properties that (a)its crystallinity is such that the half-width of X-ray diffraction ofthe (331) plane of copper is less than 0.3 deg. and (b) the variation inthickness of plated metal layer measured over the whole surface of saidsubstrate, i.e. ((maximum thickness-minimum thickness)/averagethickness), is not greater than 0.4.

The seventh invention among the inventions belonging to the first groupis concerned with a printed circuit board comprising an interlayer resininsulating layer on a substrate board for the formation of a conductorcircuit and, as disposed on top of said interlayer resin insulatinglayer, a copper-film conductor circuit, with via holes provided in saidinterlayer resin insulating layer interconnecting said conductorcircuits,

wherein said copper film has properties that (a) its crystallinity issuch that the half-width of X-ray diffraction of the (331) plane ofcopper is less than 0.3 deg. and (b) the variation in thickness of saidcopper film (electroplated copper layer) measured over the whole surfaceof said substrate, i.e. ((maximum thickness-minimum thickness)/averagethickness), is not greater than 0.4.

The copper film in the above sixth and seventh inventions is preferablyfurther has its percent elongation of not less than 7%.

The inventions of the first group relate broadly to a technology forfabricating conductor circuits for semiconductor devices and printedcircuit boards and an electroplating technology such that intermittentelectroplating is performed in a plating metal ion-containing platingsolution using the substrate surface as cathode and the plating metal asanode with the voltage between said anode and cathode being keptconstant.

The intermittent electroplating described above insures a uniformplating thickness. The reason seems to be that while the plating metaldeposit is preferentially dissolved by the spike current flowingmomentarily toward the anode in the marginal area of the substrate boardsurface and around the openings for via holes where the amount ofdeposition of the plating metal tends to be larger, the plating metal isprecipitated by the spike current flowing momentarily toward the cathodein the central area of the substrate surface and the interior parts ofthe via holes where the amount of plating metal deposition tends to besmaller as in the remainder of the region, with the result that a highlyuniform thickness of electrodeposition is insured.

Furthermore, intermittent electroplating results in an increasedcrystallinity of the plated metal film. The reason is suspected to bethat as the application of a voltage is interrupted, the metal ions inthe neighborhood of the interface of the substrate diffuse to maintain aconstant concentration at all times so that no defect occurs in thecrystal lattice of the precipitated metal layer, thus contributing to ahigher degree of crystallinity.

By the constant-voltage pulse plating technique in the inventions of thefirst group, which insures a uniform plate thickness, the thickness ofthe conductor circuits for circuit boards such as semiconductor devicesand printed circuit boards can be rendered uniform. Therefore, not onlyis impedance alignment facilitated but, because the thickness of theinterlayer resin insulating layer is uniform, an improved interlayerinsulation is materialized. Furthermore, because of high crystallinityand high elongation characteristics, the residual stress in the platedmetal layer is low so that even fine line-definition patterns can beprotected against peeling. Therefore, the connection reliability ofcircuits is improved.

The above intermittent electroplating process comprises application of avoltage between the cathode and anode and interruption thereof in analternating pattern, and preferably the voltage time/interruption timeratio is 0.01 to 100, the voltage time is not longer than 10 seconds andthe interruption time is not shorter than 1×10⁻¹² seconds. If thevoltage time exceeds 10 seconds, the film thickness will become unevenas it is the case with the conventional direct-current electroplating,and when the interruption time is less than 1×10⁻¹² seconds, thediffusion of metal ions will be insufficient to detract fromcrystallinity. The optimum voltage time/interruption time ratio is 0.1to 1.0.

The electroplating mentioned above is preferably copper plating, nickelplating, cobalt plating, tin plating or gold plating.

The copper plating solution is preferably an aqueous solution ofsulfuric acid and copper sulfate. The nickel plating solution may forexample be an aqueous solution of nickel sulfate, nickel chloride, andboric acid. The cobalt plating solution may be an aqueous solution ofcobalt chloride, basic cobalt carbonate and phosphorus acid. The tinplating solution may be an aqueous solution of stannous chloride. Forgold plating, an aqueous solution of gold chloride, potassium cyanideand gold metal can be used.

Since the electroplating bath need not be supplemented with a brightenerand other additives, the crystallinity of the plated metal deposit isremarkably high.

As the plating metal which serves as the anode, the metal in the form ofa ball or a rod, for instance, can be used.

The technology of manufacturing circuit boards in accordance with theinventions belonging to the first group in now described.

The substrate board which can be used includes metal, semiconductor,resin and ceramic substrates, among others.

First, the surface of the substrate board is made electricallyconductive so that it may be successfully electroplated. The techniquefor imparting electrical conductivity to a resin substrate or a ceramicsubstrate comprises forming metal layer by using an electroless plateddeposit layer or a sputter-metalized layer. As an alternative, thetechnique of incorporating a colloidal or powdery metal in the matrixresin can be used.

On the substrate rendered electrically conductive on the surface, aresist is disposed where necessary. The plating metal adheres to theconductive surface not covered with resist but exposed.

This substrate is immersed in the electroplating solution and subjectedto intermittent electroplating using the substrate as cathode and theplating metal as anode.

Referring to the inventions of the first group, the production processrelevant to cases in which the circuit board is a printed circuit boardis now described.

The substrate which can be used includes insulating substrates such as aresin substrate and a ceramic substrate.

The resin substrate mentioned above includes an insulating boardprepared by laminating prepregs each comprising a fibrous matriximpregnated with a thermosetting resin, a thermoplastic resin or athermosetting resin-thermoplastic resin complex or a copper-cladlaminate board prepared by laying up such prepregs and copper foils andhot-pressing them.

As the fibrous matrix mentioned above, glass cloth, aramid cloth, etc.can be used.

An electroless plating catalyst such as a Pd catalyst is applied to thesurface of said insulating substrate board to form an electroless platedlayer. When a copper-clad laminate board is used, the copper foil assuch can be utilized as cathode.

A plating resist is then disposed thereon. The plating resist can beformed by a process which comprises pasting a photosensitive dry filmfollowed by exposure and development or a process which comprisescoating the substrate board with a liquid resist followed by exposureand development.

The conductor circuit is formed by intermittent electroplating using theconductive layer not covered with resist but exposed, e.g. electrolessplated metal layer as cathode and the plating metal as anode.

Then, the plating resist is stripped off and the conductive layer, e.g.electroless plated metal layer, is etched off with an etching solutionto complete the conductor circuit.

As the etching solution mentioned above, an aqueous system of sulfuricacid-hydrogen peroxide, ferric chloride, cupric chloride or ammoniumpersulfate, for instance, can be used.

The following procedure is followed for the production of a multilayerprinted circuit board.

A conductor circuit-forming substrate board is first provided with aninterlayer resin insulating layer, which is then formed with openingsfor via holes. The openings are provided by exposure, development orirradiation with laser light.

For the interlayer resin insulating layer mentioned above, athermosetting resin, a thermoplastic resin, a partially photosensitizedthermosetting resin, or a complex resin comprising thereof can be used.

The above interlayer resin insulating layer can be formed by coatingwith an uncured resin or an uncured resin film by pressure bonding underheating. As an alternative, an uncured resin film carrying a metallayer, e.g. copper foil, on one side can be bonded. When such a resinfilm is used, the areas of the metal layer which correspond to via holesare etched off, followed by irradiation with a laser beam to providenecessary openings.

The above resin film formed with a metal layer may for example be acopper foil having resin film.

As the interlayer resin insulating layer mentioned above, the layerformed of an adhesive for electroless plating use can be used. Theoptimum adhesive for electroplating use is a dispersion of a cured acid-or oxidizing agent-soluble heat-resistant resin powder in asubstantially acid- or oxidizing agent-insoluble uncured heat-resistantresin. This is because upon treatment with an acid or an oxidizingagent, the heat-resistant resin particles are dissolved and removed sothat a roughened surface comprising narrow-necked bottle-like anchorscan be provided.

Referring to said adhesive for electroless plating use, the curedheat-resistant resin powder mentioned above, in particular, ispreferably {circle around (1)} a heat-resistant resin powder having anaverage particle diameter of not more than 10 μm, {circle around (2)} ablock powder available on aggregation of heat-resistant resin particleshaving an average particle diameter of not more than 2 μm, {circlearound (3)} a mixture of a heat-resistant resin powder having an averageparticle diameter of 2 to 10 μm and a heat-resistant resin powder havingan average particle diameter of not more than 2 μm, {circle around (4)}a pseudo-particle comprising a heat-resistant resin powder having anaverage particle diameter of 2 to 10 μm and at least one of aheat-resistant resin powder and an inorganic powder each having anaverage particle diameter of not more than 2 μm as adhered to thesurface of the first-mentioned resin powder, {circle around (5)} amixture of a heat-resistant resin powder having an average particlediameter of 0.1 to 0.8 μm and a heat-resistant resin powder having anaverage particle diameter of over 0.8 μm to less than 2 μm, or {circlearound (6)} a heat-resistant resin powder having an average particlediameter of 0.1 to 1.0 μm is preferred. With any of those materials, themore sophisticated anchors can be provided.

The depth of the roughened surface structure is preferably Rmax=0.01 to20 μm. This is preferred for insuring a sufficient degree of adhesion.Particularly in the semi-additive process, the depth of 0.1 to 5 μm ispreferred, for the electroless plated metal layer can then be removedwithout detracting from adhesion.

The substantially acid- or oxidizing agent-insoluble heat-resistantresin mentioned above is preferably a “complex resin comprising athermosetting resin and a thermoplastic resin” or a “complex resincomprising a photosensitive resin and a thermoplastic resin”. This isbecause while the former is highly heat-resistant, the latter is capableof forming openings for via holes by a photolithographic technique.

The thermosetting resin which can be used as above includes epoxy resin,phenolic resin and polyimide resin. For imparting photosensitivity, thethermosetting groups are acrylated with methacrylic acid or acrylicacid. The optimum resin is an acrylated epoxy resin.

As the above-mentioned epoxy resin, there can be used novolac epoxyresins such as phenol novolac resin and cresol novolac resin anddicyclopentadiene-modified alicyclic epoxy resin.

As the thermoplastic resin, there can be used polyethersulfone (PES),polysulfone (PSF), polyphenylenesulfone (PPS), polyphenylene sulfide(PPES), polyphenyl ether (PPE), polyetherimide (PI) and fluororesin.

The blending ratio of the thermosetting resin (photosensitive resin) tothe thermoplastic resin, i.e. thermosetting (photosensitive)resin/thermoplastic resin, is. preferably 95/5 to 50/50. This rangecontributes to a high level of toughness without compromise in heatresistance.

The blending weight ratio of said heat-resistant resin powder ispreferably 5 to 50 weight % based on the solid matter of theheat-resistant resin matrix. The more preferable ratio is 10 to 40weight %.

The heat-resistant resin powder is preferably an amino resin (melamineresin, urea resin, guanamine resin) or an epoxy resin, for instance.

Further, an electroless plated metal layer is formed over saidinterlayer resin insulating layer (on the copper foil when aresin-containing copper foil is used) inclusive of surface of openingsand after placement of a resist, electroplating is performed to providea conductor circuit and via holes.

The electroplating is performed intermittently using said electrolessplated metal layer as cathode and the plating metal as anode with thevoltage between the anode and cathode being kept constant.

Then, the resist is stripped off and the electroless plated metal layeris etched off.

The circuit board and printed circuit board formed by the electroplatingprocess according to the first group of the present inventions, in whichthe conductor wiring or conductor circuit is made of copper, shouldsatisfy the following conditions (a) and (b).

Thus, (a) as to crystallinity, the half-width of X-diffraction of the(331) plane of copper is not greater than 0.3 deg, and (b) the variationin plating thickness of the copper layer (electrolated copper layer) asmeasured all over the surface of said substrate board ((maximumthickness-minimum thickness)/average thickness) is not greater than 0.4.

When the half-width of X-ray diffraction of the (331) plane of copper is0.3 deg. or larger, the residual stress will be increased and, in thecase of a delicate pattern, there will be a risk for peeling. If thevariation ((maximum thickness-minimum thickness)/average thickness) isgreater than 0.4, impedance alignment may hardly be obtained.

The reason for selection of the (331) plane of copper is that this isthe plane revealing the most striking change in crystallinity in X-raydiffraction analysis.

The percent elongation mentioned above for the copper layer ispreferably not less than 7%. If the elongation is less than 7%, cracksare liable to develop on cold thermal shock.

In the inventions of the first group, the purity of copper deposited isas high as 99.8% or more. Therefore, the inherent ductility of copper isfully expressed to provide a high elongation rate.

The circuit board mentioned above includes printed circuit boards, ICchips and semiconductor devices such as LSI.

The first invention among inventions belonging to a second group isconcerned with an electroless plating solution comprising an aqueoussolution containing 0.025 to 0.25 mol/L of a basic compound, 0.03 to0.15 mol/L of a reducing agent, 0.02 to 0.06 mol/L of copper ion and0.05 to 0.30 mol/L of tartaric acid or a salt thereof.

The second invention among inventions of the second group is concernedwith an electroless plating solution comprising an alkaline compound, areducing agent, copper ion, tartaric acid or a salt thereof and at leastone metal ion species selected from the group consisting of nickel ion,cobalt ion and iron ion.

The preferred specific gravity of the electroless plating solutionsaccording to the above first and second inventions is 1.02 to 1.10.

Furthermore, the preferred temperature of those electroless platingsolutions is 25 to 40° C. In addition, the copper deposition rate ofthose electroless plating solutions is preferably 1 to 2 μm/hour.

The third invention among inventions of the second group is concernedwith an electroless plating process which comprises immersing asubstrate in the electroless plating solution of said first or secondinvention and performing electroless copper plating with the depositionrate set to 1 to 2 μm/hour.

In the above electroless plating process, said substrate is preferablyprovided with a roughened surface in advance.

The fourth invention among inventions of the second group is concernedwith a process for manufacturing a printed circuit board comprisingimmersing a resin insulating substrate board in the electroless platingsolution of said first or second invention and performing electrolesscopper plating with the deposition rate set to 1 to 2 μm/hour to providea conductor circuit.

The fifth invention among inventions of the second group is concernedwith a printed circuit board comprising a resin insulating substrateboard having a roughened surface and, as electroless plated layerthereon, a conductor circuit, wherein said electroless plated layer hasa stress value of 0 to +10 kg/mm².

The sixth invention among inventions of the second group is concernedwith a printed circuit board comprising a resin insulating substrateboard having a roughened surface and, as an electroless plated layerthereon, a conductor circuit, wherein said electroless plated layer iscomplementary to said roughened surface and relatively increased inthickness in convex areas of the roughened surface as compared withconcave areas of said surface.

The concave and convex areas mentioned above mean the concave and convexparts of the primary anchor and do not refer to the secondary anchorformed on the convex part thereof or the like (ref. FIG. 16).

The seventh invention among inventions of the second group is concernedwith a printed circuit board which comprises a substrate board formedwith a lower conductor circuit, an interlayer resin insulating layerthereon and an upper conductor circuit as built up with said lowerconductor circuit connected to said upper conductor circuit through viaholes, wherein said upper-layer conductor circuit comprises at least anelectroless plated metal film, said interlayer resin insulating layerhas a roughened surface, said electroless plated metal film iscomplementary to said roughened surface throughout and the bottom partsof said via holes are also provided with a electroless plated layer in athickness equal to 50 to 100% of the electroless plated layer formed onsaid interlayer resin insulating layer.

The eighth invention among inventions of the second group is concernedwith a printed circuit board comprising a resin insulating substrateboard and as built thereon a conductor circuit comprising at least anelectroless plated metal layer, wherein said electroless plated metallayer comprises copper and at least one metal selected from the groupconsisting of nickel, iron and cobalt.

In the printed circuit board according to the above eighth invention ofthe second group, the preferred content of said at least one metalselected from nickel, iron and cobalt is 0.1 to 0.5 weight %.

The electroless plating solution according to the first invention amonginventions of the second group comprises an aqueous solution containing0.025 to 0.25 mol/L of a basic compound, 0.03 to 0.15 mol/L of areducing agent, 0.02 to 0.06 mol/L of copper ion and 0.05 to 0.3 mol/Lof tartaric acid or a salt thereof.

The electroless plating solution according to the second invention amonginventions of the second group comprises an aqueous solution containinga basic compound, a reducing agent, copper ion, tartaric acid or a saltthereof and at least one ion species selected from the group consistingof nickel ion, cobalt ion and iron ion.

Since those electroless plating solutions contain tartaric acid or itssalt, the amount of hydrogen uptake in the plating metal deposit is sosmall that a tensile stress is generated in the plated metal layer.Since its absolute value is small compared with the conventional case(when EDTA is used as a complexing agent) but appropriate, the platedmetal layer adheres intimately to the substrate and hardly peels offfrom the substrate.

Furthermore, by controlling the proportion of said basic compound withinthe range of 0.025 to 0.25 mol/L and that of said reducing agent withinthe range of 0.03 to 0.15 mol/L, the deposition rate of the platingsolution can be reduced to 1 to 2 μm/hr. Therefore, when a plating metalis deposited in the openings for via holes, the copper ions are allowedto diffuse far enough down the openings for via holes so that asufficiently thick plated metal film can be formed even within fine viaholes.

Since the electroless plating solution according to the above secondinvention of the second group contains at least one metal ion speciesselected from the group consisting of nickel ion, cobalt ion and ironion in addition to tartaric acid or a salt thereof, the evolution ofhydrogen is suppressed with the result that an appropriate tensilestress is generated in the plated metal layer to insure a good adhesionto the substrate and, hence, exfoliation of the plated metal from thesubstrate is hard to take place.

The specific gravity of those electroless plating solutions ispreferably adjusted to 1.02 to 1.10. This is because a plating metal canthen be precipitated in the fine openings for via holes.

The preferred temperature of those electroless plating solutions is 25to 40° C. If the temperature is excessively high, the deposition will beaccelerated so much that the plating metal can hardly be depositedwithin fine openings for via holes. If the temprature is less than 25°C., it takes so much time to deposit the plated metal layer, thereforthe temperature is not practical.

Furthermore, the above electroless plating solutions preferably contain0.01 to 0.05 weight % of nickel ion, iron ion and/or cobalt ion.

By setting the concentration of nickel and/or other ion within the aboverange, the concentration of said at least one metal ion species selectedfrom the group consisting of nickel, iron and cobalt ions can becontrolled within the range of 0.1 to 0.5 weight % to thereby provide aplated metal film which is hard enough and shows good adhesion to theresin insulating layer.

Referring to the electroless plating solution according to the firstinvention among said inventions of the second group, said basic compoundmay for example be sodium hydroxide, potassium hydroxide or ammonia.

The reducing agent mentioned above includes formaldehyde, sodiumhypophosphite, NaBH₄ and hydrazine.

The compound mentioned above as a copper ion includes copper sulfate andcopper chloride.

The above-mentioned salt of tartaric acid includes the correspondingsodium salt and potassium salt and any of those salts may be the saltderived by substituting only one of the available two carboxyl groupswith the above-mentioned particular metal or the salt derived bysubstituting both the carboxyl groups with the above-mentioned metal.

Referring to the electroless plating solution according to the abovesecond invention of the second group, the compound for providing saidnickel ion includes nickel chloride and nickel sulfate; the compound forproviding said cobalt ion includes cobalt chloride; and the compoundproviding for said iron ion includes iron chloride.

The third invention of the second group is concerned with an electrolessplating process which comprises immersing a substrate in saidelectroless plating solution and performing copper electroless platingat the deposition rate set to 1 to 2 μm/hr as mentioned above.

The fourth invention of the second group is concerned with a process formanufacturing a printed circuit board which comprises immersing a resininsulating substrate board in said electroless plating solution andperforming copper electroless plating by the above-mentioned electrolesscopper plating process to provide a conductor circuit.

The resin insulating substrate board mentioned above means not only aresin insulating substrate board not formed with a conductor circuit buta resin insulating substrate board formed with a conductor circuit and,in superimposition, further with an interlayer resin insulating layerhaving openings for via holes.

In the above electroless plating process or in the above process formanufacturing a printed circuit board, the surface of resin insulatinglayer constituting said substrate and the resin insulating substrate ispreferably a roughened surface.

The roughened surface mentioned above comprises concave areas and convexareas and the plating metal is deposited tracing those concave andconvex areas but the thickness of the deposit is larger in the convexareas of the roughened surface than in the concave areas thereof andthis thickness profile offers the following advantages.

Thus, in the process generally called the semi-additive process whichcomprises disposing a plating resist on an electroless plated metallayer, performing electroplating to form a thick plated metal film,stripping off said plating resist and etching the electroless platedmetal layer beneath the plating resist, the etching operation is easierwhen the thichness of the electroless plated metal film is relativelythin in the concave areas as compared with the convex areas and thewhole plated metal deposit can be easily removed by this etching withoutleaving unetched areas, with the result that the insulation reliabilityof the resulting circuit is very satisfactory.

The printed circuit board fabricated by the process for manufacturing aprinted circuit board according to the fourth invention of the secondgroup has the following characteristics.

Thus, the printed circuit board according to the fifth invention of thesecond group comprises a resin insulating substrate board having aroughened surface and as built thereon a conductor circuit comprising atleast an electroless plated metal film,

wherein said electroless plated metal film has a stress value of 0 to+10 kg/mm².

The sign of the above stress value is positive, i.e. +, which means thata tensile stress has been generated in the above-mentioned plated metalfilm. This stress can be measured with a spiral stress meter(manufactured by Yamamoto Plating Co., Ltd.).

Moreover, within the above stress range, the plated metal film does notundergo blistering or peeling so that the connection reliability of theconductor circuits is high.

The printed circuit board according to the sixth invention of the secondgroup is a printed circuit board comprising a resin insulating substrateboard formed with a roughened surface and as built thereon a conductorcircuit comprising at least an electroless plated metal film, whereinsaid electroless plated metal film is complementary to said roughenedsurface and the thickness of said electroless plated metal film isrelatively thick in the convex areas of the roughened surface comparedwith the concave areas thereof (that is to say, the electroless platedmetal film in the concave areas is relatively thin as compared with theconvex areas thereof).

Therefore, when a conductor circuit is to be formed by the semi-additiveprocess mentioned above, the electroless plated metal film in theconcave areas of said roughened surface, which is thinner than that inthe convex areas, can be more readily and completely stripped off, withthe result that the problem of unetched residues is obviated in theetching step and a high inter-conductor insulation dependability isassured.

The printed circuit board according to the seventh invention of thesecond group is concerned with a circuit board which comprises asubstrate board carrying a lower conductor circuit built thereon, aninterlayer resin insulating layer and an upper conductor circuit asbuilt up with said lower conductor circuit and upper conductor circuitbeing interconnected by via holes,

wherein said upper conductor circuit comprises at least electrolessplated metal film, said interlayer resin insulating layer has aroughened surface, said electroless plated metal film is complementaryto said roughened surface, and bottoms of said via holes also carry theelectroless plated metal film in a thickness equal to 50 to 100% of thethickness of the electroless plated metal film on said interlayer resininsulating layer.

The above printed circuit board is fabricated using the above-describedelectroless plating solution and, therefore, via holes can be providedbecause, even when the openings for via holes are as fine as 80 μm orless in diameter, a sufficiently thick plated metal film can be formedon the hole bottoms.

The printed circuit board according to the eighth invention of thesecond group comprises a resin insulating substrate board and, as builtthereon, a conductor circuit comprising at least an electroless platedmetal film, wherein said electroless plated metal film comprises copperand at least one metal species selected from the group consisting ofnickel, iron and cobalt.

Here, addition of a salt of such a metal ion inhibits the uptake ofhydrogen into the plated metal to reduce the compressive stress ofplating so that the resulting film may have an improved adhesion to theresin insulating layer. Furthermore, those metals form alloys withcopper to increase the hardness of the plated metal film, thuscontributing further to the adhesion to the resin insulating layer.

An electrodeposition layer which is high in hardness and adhesion to theresin insulating layer can be obtained when the content of said at leastone metal species selected from among nickel, iron and cobalt is withinthe range of 0.1 to 0.5 weight %.

The technology for manufacture of printed circuit boards according tothe inventions of the second group is now described, taking thesemi-additive process as an example.

-   (1) First, a substrate board carrying an inner-layer copper pattern    (lower conductor circuit) on the surface of a core board is    constructed.

Formation of the conductor circuit on the core board can be achievedtypically by a process which comprises etching a copper-clad laminateboard according to a predetermined pattern, a process which comprisesdepositing an electroless plating adhesive layer on a glass-epoxysubstrate board, polyimide substrate board, ceramic substrate board ormetal substrate board, roughening the adhesive layer to impart aroughened surface and performing electroless plating, or a process whichcomprises performing electroless plating all over said roughenedsurface, disposing a plating resist, performing electroplating over theareas other than the plating resist areas, stripping off the platingresist and performing etching to provide a conductor circuit comprisingthe electroplated metal film and the electroless plated metal film(semi-additive process).

In addition, the surface of the conductor circuit of the above circuitboard may be formed with a roughened surface or a roughened layer.

The roughened surface or roughened layer mentioned above is preferablyformed by any of sanding, etching, blackening-reduction, and platingtechniques.

Blackening-reduction, among the above techniques, is preferably carriedout by a method using a blackening bath (oxidizing bath) comprising anaqueous solution of NaOH (20 g/l), NaClO₂ (50 g/l) and Na₃PO₄ (15.0 g/l)and a reducing bath comprising an aqueous solution of NaOH (2.7 g/l) andNaBH₄ (1.0 g/l).

The preferred procedure for forming a roughened layer by a platingtechnique comprises performing electroless plating using an electrolessplating solution (pH=9) containing copper sulfate (1 to 40 g/l), nickelsulfate (0.1 to 6.0 g/l), citric acid (10 to 20 g/l), sodiumhypophosphite (10 to 100 g/l), boric acid (10 to 40 g/l) and asurfactant (Surfinol 465, Nisshin Chemical Industries, Ltd.) (0.01 to 10g/l) to provide a roughened layer composed of Cu—Ni—P alloy.

The crystal of the plated metal deposit formed within the above rangehas an acicular structure which has an excellent anchor effect. Thiselectroless plating bath may contain a complexing agent and variousadditives in addition to the above compounds.

The method for providing a roughened layer by etching includes a processwhich comprises permitting an etching solution containing a cupriccomplex compound and an organic acid to act upon the surface of theconductor circuit in the presence of oxygen to thereby roughen saidsurface.

In this case, etching proceeds according to the chemical reactionsrepresented by the following expression (1) and expression (2).

(wherein A represents a complexing agent (which functions as a chelatingagent) and n represents a coordination number).

The cupric complex mentioned above is preferably a cupric azole complex.This cupric azole acts as an oxidizing agent which oxidizes metalliccopper or the like. The azole may for example be a diazole, a triazoleor a tetrazole. Particularly preferred species are imidazole,2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole,2-phenylimidazole, 2-undecylimidazole, etc. The cupric azole complexcontent of said etching solution is preferably 1 to 15 weight %. Withinthis range, the complex is good in solubility and stability and capableof dissolving even a noble metal, such as Pd, which constitutes thecatalyst nucleus.

To insure dissolution of copper oxide, an organic acid is used inassociation with the cupric azole complex. The organic acid includesformic acid, acetic acid, propionic acid, butyric acid, valeric acid,caproic acid, acrylic acid, crotonic acid, oxalic acid, malonic acid,succinic acid, glutaric acid, maleic acid, benzoic acid, glycolic acid,lactic acid, malic acid and sulfamic acid. Those acids may be used eachindependently or in a combination of two or more species.

The preferred organic acid content of the etching solution is 0.1 to 30weight %. In this range, the solubility of oxidized copper and thesolution stability can be sufficiently insured. As expressed by theabove expression (2), the cuprous complex generated is dissolved underthe influence of the acid and binds oxygen to form the cupric complex,thus contributing to the oxidation of copper again.

To assist in the dissolution of copper and the oxidizing action of theazole compound, the etching solution mentioned above may be supplementedwith a halide ion, e.g. fluoride ion, chloride ionorbromide ion. Thehalide ion may also be supplied by adding hydrochloric acid, sodiumchloride or the like. The halide ion content of the etching solution ispreferably 0.01 to 20 weight %. In this range, a good adhesion can beinsured between the roughened surface and the interlayer resininsulating layer.

In preparing the etching solution, said cupric azole complex and organicacid (where necessary, one having a halide ion is used) are dissolved inwater. As said etching solution, a commercial etching solution, forexample “Meck Etch Bond”, trade mark, manufactured by Meck Co., Ltd.,can be used. The etching amount, when the above etching solution isused, is preferably 0.1 to 10 μm, the optimum range being 1 to 5 μm. Ifthe etching amount exceeds 10 μm, a connection defect occurs between theroughened surface and the via hole conductor. On the other hand, if theetching amount is less than 0.1 μm, the adhesion to the interlayer resininsulating layer to be built thereon will not be sufficiently high.

The roughened layer or roughened surface may be covered with a layermade of a metal having an ionization tendency greater than copper butnot greater than titanium or a noble metal layer (hereinafter referredto as the metal layer). The metal mentioned above includes titanium,aluminum, zinc, iron, indium, thallium, cobalt, nickel, tin, lead andbismuth. The noble metal includes gold, silver, platinum and palladium.Those metal species may be used either independently or in a combinationof two or more species to form a plurality of layers.

Such a metal layer covers the roughened layer and roughens theinterlayer resin insulating layer to prevent local electrode reactionsand thereby protect the conductor circuit against dissolution. Thepreferred thickness of such a metal layer is 0.1 to 2 μm.

Among the metals used to constitute said metal layer, tin is preferred.This is because tin may form a thinner layer on lectroless substitutedplated layer faithfully tracing the roughened layer.

To form a metal layer composed of tin, substitution plating is carriedout using a tin borofluoride-thiourea containing solution or a tinchloride-thiourea containing solution. In this case, an Sn layer about0.1 to 2 μm thick is formed by the Cu—Sn substitution reaction. To forma metal layer composed of a noble metal, sputtering or vapor depositioncan be used, for instance.

The core substrate board may be equipped with plated-through holes sothat the wiring layer on the face side and the reverse side may beelectrically connected through said plated-through holes.

Moreover, between the plated-through holes and conductor circuits of thecore board, a low-viscosity resin such as bisphenol F epoxy resin may befilled in to insure evenness.

-   (2) Then, the substrate board prepared as above in (1) is coated    with a organic solvent-containing resin composition for preparation    of a roughened surface and the coat is dried to provide a layer of    the resin composition for preparation of a roughened surface.

The resin composition for preparation of a roughened surface mentionedabove is preferably a composition comprising an uncured heat-resistantresin matrix, which is hardly soluble in a roughing solution comprisingat least one member selected from the group consisting of an acid, analkali and an oxidizing agent, and, as dispersed therein, a substancesoluble in said roughening solution comprising at least one memberselected from the group consisting of an acid, an alkali and anoxidizing agent.

The terms “hardly soluble” and “soluble” are used here in connectionwith the inventions of the second group to mean that, when immersed inthe same roughening solution for the same duration of time, thesubstance which dissolves at a relatively high dissolution rate isdescribed as being “soluble” and the one which shows a relatively lowdissolution rate is described as being “hardly soluble”, forconvenience's sake.

As the heat-resistant resin matrix mentioned above, a thermosettingresin or a complex resin composed of a thermosetting resin (inclusive ofone in which some of the thermosetting groups have been photosensitized)and a thermoplastic resin, for instance, can be used.

The thermosetting resin mentioned above includes epoxy resin, phenolicresin, polyimide resin and thermosetting polyolefin resins.Photosensitization of the thermosetting resin, referred to above, can beachieved by (meth) acrylating the thermosetting groups of the resin withmethacrylic acid or acrylic acid. The most preferred example is a(meth)acrylated epoxy resin.

The epoxy resin mentioned above includes novolac epoxy resin andalicyclic epoxy resin.

The thermoplastic resin mentioned above includes polyethersulfone,polysulfone, polyphenylenesulfone, polyphenylene sulfide, polyphenylether and polyetherimide.

The above-mentioned substance soluble in said roughening solutioncomprising at least one member selected from the group consisting of anacid, an alkali and an oxidizing agent is preferably at least one memberselected from the group consisting of an inorganic powder, a resinpowder, a metal powder, a rubber powder, a liquid-phase resin and aliquid -phase rubber.

The inorganic powder mentioned above includes powders of silica,alumina, calcium carbonate, talc and dolomite. Those substances can beused either independently or in a combination of two or more species.

The alumina powder mentioned above can be dissolved and removed withfluoric acid and the calcium carbonate powder can be dissolved andremoved using hydrochloric acid. The sodium-containing silica anddolomite can be dissolved and removed with an aqueous alkaline solution.

The resin powder mentioned above includes amino resin (e.g. melamineresin, urea resin, guanamine resin, etc.), epoxy resin andbismaleimide-triazine resin. Those resins can be used eitherindependently or in a combination of two or more species.

As said epoxy resin, either the resin soluble in acids and oxidizingagents or the resin hardly soluble therein can be freely prepared byselecting kind of oligomers and curing agents. For example, whereas theresin obtainable by curing bisphenol A epoxy resin with an amine seriescuring agent is readily soluble in chromic acid, the resin obtainable bycuring cresol novolac epoxy resin with an imidazole series curing agentis hardly soluble in chromic acid.

It is essential that said resin powder be cured in advance. Unless curedahead of time, the resin powder dissolves in the solvent for the resinmatrix to give a homogeneous mixture so that the resin powder cannot beselectively dissolved off with an acid or an oxidizing agent.

The metal powder mentioned above includes powders of gold, silver,copper, tin, zinc, stainless steel and aluminum. Those metal powders canbe used either independently or as a mixture of two or more species.

The rubber powder mentioned above includes acrylonitrile-butadienerubber, polychloroprene rubber, polyisoprene rubber, acryl rubber,polysulfide-vulcanized hard rubber, fluoro rubber, urethane rubber,silicone rubber and ABS resin powders. Those rubber powders can be usedeither independently or in a combination of two or more species.

As the liquid resin mentioned above, a solution of said thermosettingresin in uncured state can be used. For example, a mixture of an uncuredepoxy oligomer and an amine series curing agent can be mentioned.

As the liquid rubber, a solution of the above-mentioned rubbers inuncured state can be used.

In preparing said photosensitive resin composition using said liquidresin or liquid rubber, these substances should be selected to insurethat said heat-resistant resin matrix and the selected soluble substancewill not form a homogeneous mixture (i.e. but will form discretephases).

By using the heat-resistant matrix resin and soluble substance selectedaccording to the above criterion, there can be obtained a photosensitiveresin composition in which many islands of said liquid resin or liquidrubber are scattered in an ocean of said heat-resistant resin orconversely islands of said heat-resistant resin matrix are scattered inan ocean of said liquid resin or liquid rubber.

After curing of such a photosensitive resin composition, the liquidresin or liquid rubber forming said ocean or said islands, as the casemaybe, is removed, whereupon the objective roughened surface isobtained.

The acid which can be used as said roughening solution includesphosphoric acid, hydrochloric acid, sulfuric acid and a variety oforganic acids such as formic acid and acetic acid, among others,although an organic acid is preferably used. This is because when anorganic acid is used for roughening, it does hardly corrode the metalconductor layer exposed from via holes.

As the oxidizing agent mentioned above, chromic acid or an aqueoussolution of an alkali permanganate (e.g. potassium permanganate), forinstance, is preferably selected.

The alkali mentioned hereinbefore is preferably an aqueous solution ofsodium hydroxide or potassium hydroxide, for instance.

In the second group of the present invention, wherein said inorganicpowder, metal powder or resin powder is used, the average particlediameter of the powder is preferably not greater than 10 μm.

Particularly, even if a mixed powder is not greater than 2 μm in averageparticle diameter, the use of the mixed powder which actually comprisesa coarse powder having a relatively large average particle diameter anda fine powder having a relatively small average particle diameter willeliminate residues of undissolved electroless plated metal, reduce theamount of the palladium catalyst underneath the plating resist and,moreover, provide a shallow but complex roughened surface. By providingsuch a roughened surface of complexity, a practically useful peelstrength can be imparted even with a shallow roughened depth profile.

The reason why a shallow but complex roughened surface can be providedby using said coarse powder and fine powder in combination is thatbecause the average particle diameter of even the coarse powder is lessthan 2 μm, the anchors available upon dissolution and removal of theparticles are small in depth and, at the same time, because the particleremoved is actually a mixture of a coarse powder having a relativelylarge particle size and a fine powder having a relatively small particlesize, the resulting roughened surface becomes a complex texture.

Furthermore, since the average particle diameter of even the coarsepowder used is less than 2 μm, there is no risk for clearances arisingfrom excessive roughening, so that the resulting interlayer resininsulating layer is excellent in interlayer insulation.

It is preferable that the average particle diameter of said coarsepowder be over 0.8 μm but less than 2.0 μm and that of said fine powderbe 0.1 to 0.8 μm.

Within the above range, the depth of said roughened surface isapproximately Rmax=3 μm, and in the semi-additive process, it is notonly easy to etch off the electroless plated metal deposit but also easyto remove the Pd catalyst beneath the electroless plated metal depositand, moreover, a practically useful peel strength of 1.0 to 1.3 kg/cmcan be insured.

The organic solvent content of the above resin composition forpreparation of roughened surfaces is preferably not more than 10 weight%.

Coating with the resin composition for preparation of roughened surfacescan be carried out using a roll coater or a curtain coater, forinstance.

-   (3) The resin composition layer for preparation of roughened    surfaces formed in (2) above is dried to a semi-hardened state and,    then, provided with openings for via holes.

In the dry state of the resin composition layer for preparation ofroughened surface, the thickness of the resin composition layer on theconductor circuit pattern is small while the thickness of the plainlayer having large area is large and, moreover, the interlayer resininsulating layer has been corrugated due to the non-uniformity in levelof the conductor circuit area and the non-circuit area. Therefore, thesurface of the interlayer resin insulating layer is preferablysmoothened by pressing with a metal plate or roll under heating.

The openings for via holes are formed by a process which comprisesexposing the resin composition layer for preparation of roughenedsurface imagewise to ultraviolet or other light and developing. Forexposure and development, a photomask (preferably a glass substrate)marked with a pattern of black dots in the areas corresponding to saidopenings for via holes is placed with its patterned side in intimatecontact with the roughened surface-forming resin composition layer and,in this state, exposure and development are carried out.

-   (4) Then, the roughened surface-forming resin composition layer is    cured to provide an interlayer resin insulating layer, which is then    roughened.

The roughening treatment comprises removing said at least one solublesubstance selected from the group consisting of an inorganic powder, aresin powder, a metal powder, a rubber powder, a liquid resin and aliquid rubber, which exists on the surface of said interlayer resininsulating layer with a roughening solution such as said acid, oxidizingagent or alkali. The depth of roughening is preferably about 1˜5 μm.

-   (5) Then, a catalyst nucleus is applied to the circuit board    comprising the roughened interlayer resin insulating layer.

This application of a catalyst nucleus is preferably carried out using anoble metal ion or a noble metal colloid. Generally, palladium chlorideor colloidal palladium is used. A heat treatment is preferably carriedout for immobilizing the catalyst nucleus. The preferred catalystnucleus is palladium.

-   (6) Then, an electroless plating metal is deposited all over the    roughened surface. As the electroless plating solution, the    above-described electroless plating solution according to the second    group of the present invention is employed.

With regard to the plating bath formula, a preferred example is anaqueous solution containing NiSO₄ (0.001 to 0.003 mol/L), copper sulfate(0.02 to 0.04 mol/L), tartaric acid (0.08 to 0.15 mol/L), sodiumhydroxide (0.03 to 0.08 mol/L) and 37% formaldehyde (0.03 to 0.06mol/L). The thickness of the electroless metal deposit is preferably 0.1to 5 μm, more preferably 0.5 to 3 μm.

-   (7) Then, a photosensitive resin film (dry film) is laminated onto    the electroless plated metal layer and a photomask (preferably a    glass substrate) marked with a plating resist pattern is set in    intimate contact with the photosensitive resin film. Thereafter,    exposure and development are carried out to form a plating resist    pattern.-   (8) Then, the resist-free surface is electroplated to form the    conductor circuit and via holes.

As the above-mentioned electroplating, copper electroplating ispreferred to use and the plating thickness is preferably 1 to 20 μm.

-   (9) After removal of the plating resist, the electroless plated    metal deposit is removed using an etching solution containing    sulfuric acid-hydrogen peroxide mixture, sodium persulfate, ammonium    persulfate, ferric chloride or cupric chloride to provide an    isolated conductor circuit. Since the palladium catalyst nucleus is    simultaneously removed by said etching, it is not particularly    necessary to remove the palladium catalyst nucleus using chromic    acid or the like.-   (10) Then, the surface of the conductor circuit is provided with a    roughened layer or roughened surface.

Formation of said roughened layer or roughened surface is carried out bythe procedure described above in (1).

-   (11) Then, using said resin composition for preparation of roughened    surface, an interlayer resin insulating layer is formed on the above    substrate board in the same manner as described above.-   (12) Then, the steps (3) to (10) are repeated to form an upper-layer    conductor circuit and, then, planar conductor pads to serve as    solder pads, via holes, etc. are formed. Finally, a solder resist    layer and solder bumps are formed to complete the manufacture of a    printed circuit board. While the above description pertains to the    semi-additive process, the full-additive process may likewise be    used.

The first invention of the third group is concerned with a process formanufacturing a multilayer printed circuit board comprising at least thefollowing steps (1) to (5).

-   (1) A step for thinning the copper foil of a copper-clad laminate by    etching-   (2) A step for piercing through holes in said copper-clad laminate-   (3) A step for forming plated-through holes in the resulting holes    by plating said copper-clad laminate-   (4) A step for constructing a conductor circuit by pattern-etching    the copper foil and plated metal layer on the surface of said    copper-clad laminate-   (5) A step for building up an interlayer resin insulating layer and    a conductor layer in an alternate fashion over said conductor    curcuit.

The second invention of the third group is concerned with a process formanufacturing a multilayer printed circuit board comprising at least thefollowing steps (1) through (7).

-   (1) A step for thinning the copper foil of a copper-clad laminate    board by etching-   (2) A step for piercing through holes in said copper-clad laminate    board-   (3) A step for depositing a conductor layer on said copper-clad    laminate board-   (4) A step for disposing a resist over the area other than the    conductor circuit-forming and the area of plated-through hole-   (5) A step for forming a conductor circuit and plated-through holes    by plating the resist-free area-   (6) A step for stripping the resist off and etching the conductor    film and copper foil underneath the resist-   (7) A step for building up an interlayer resin insulating layer and    a conductor layer in an alternate fashion over said conductor    circuit.

In the above process for manufacturing a multilayer printed circuitboard, the step of piercing through holes in said copper-clad laminatecan be carried out using a laser or a drill.

In the step of thinning the copper foil of said copper-clad laminateboard by etching in the first and second inventions of the third group,the thickness of copper foil is reduced preferably to 1 to 10 μm, morepreferably 2 to 7 μm.

The third invention of the third group is concerned with a multilayerprinted circuit board comprising a core board having a conductor circuitand, as disposed on said conductor circuit, a buildup wiring layersobtainable by building up an interlayer resin insulating layer and aconductor layer alternately, with via holes interconnecting theconductor layers, which has technical properties that the thickness ofthe conductor circuit on the core board is restricted to a maximum of 10μm over the thickness of the conductor layer on the than 7 μm.

It is also preferable that the above-mentioned interlayer resininsulating layer.

Preferably the thickness of the conductor circuit on said core board isnot greater by more that said core board comprises a copper-cladlaminate and that the conductor circuit on the core board comprises thecopper foil of said copper laminate and a plated metal layer.

The fourth invention of the third group is concerned with a process formanufacturing a multilayer printed circuit board which comprisesthinning the copper foil of a copper-clad laminate by etching,pattern-etching the copper foil of said copper-clad laminate board toform a conductor circuit, and building up an interlayer resin insulatinglayer and a conductor layer in an alternate fashion over said conductorcircuit, wherein the thickness of the conductor circuit on said coreboard is restricted to a maximum of 10 μm in excess over the thicknessof the conductor layer on the interlayer resin insulating layer.

In the process for manufacturing a multilayer printed circuit boardaccording to the first invention of the third group, the thickness ofthe copper foil of a copper-clad laminate is reduced by etching. Then,plating is performed to form plated-through holes. In this step, aplated metal film is formed on the copper foil. The copper foil carryingthis plated metal film is pattern-etched to construct a conductorcircuit. Since the copper foil has been reduced in thickness in advance,the combined thickness of the copper foil and plated metal film toconstitute a conductor circuit is small so that a fine-line circuit canbe formed by pattern etching.

Furthermore, while interlayer resin insulating layers and conductorlayers are built up in alternate succession on the copper-clad laminateforming said conductor circuit, the combined thickness of the copperfoil and plated metal film forming said conductor circuit will not besmall and much different from the thickness of the conductor layer onthe interlayer resin insulating layer so that an impedance alignment canbe obtained between said conductor circuit on core board and theconductor layer on the interlayer resin insulating layer. As a result,high-frequency characteristic of the multilayer printed circuit boardcan be improved.

In the process for manufacturing a multilayer printed circuit boardaccording to said second invention of the third group, which comprisesthinning the copper foil of a copper-clad laminate by etching, forming auniform conductor film thereon, plating the resist-free area toconstruct a conductor circuit, stripping the resist off and etching theconductor film and copper foil under the resist, the copper foil isthinned by etching in the first place so that the combined thickness ofconductor film and copper foil is reduced, contributing to theimplementation of an elaborate circuit pattern.

Furthermore, while an interlayer resin insulating layer and a conductorlayer are thus built up alternately on a copper-clad laminate formedwith said conductor circuit, the combined thickness of the copper foiland plated metal film forming said conductor circuit has been reducedand is not much different from the conductor layer on the interlayerresin insulating layer, with the result that an impedance alignment isobtained between the conductor circuit on the core board and theconductor layer on the interlayer resin insulating layer, thuscontributing an improved high-frequency characteristic of the multilayerprinted circuit board.

In the above step of piercing through holes in said copper-cladlaminate, when piercing through holes by means of a laser beam, forinstance, to thin the copper foil by etching in advance suppresses theconduction of laser light as a thermal energy through the copper foil,so that the through holes can be easily pierced by a laser beam.

In the case of piercing through holes with a drill, through holes canalso be easily pierced in the copper-clad laminate.

In the above step of thinning the copper foil of the copper-cladlaminate by etching, controlling the thickness of the copper foil withinthe range of 1 to 10 μm leads to a reduced combined thickness of thecopper foil and plated metal film constituting the conductor circuit sothat an elaborate circuit can be formed by pattern etching. Moreover,since the differential in thickness between the conductor circuit oncore board and the conductor layer on the interlayer resin insulatinglayer can be set small, the impedances of both layers can be easilyaligned.

The optimum copper foil thickness is 2 to 7 μm. Generally, a resinfiller is filled in between the conductor circuits formed on the surfaceof a core board so as to prepare a flat surface and, then, an interlayerresin insulating layer is formed thereon but, in accordance with thisinvention, the interlayer resin insulating layer naturally assumes aflat surface in sole dependence on the inherent levelling function ofthe interlayer resin insulating layer.

Furthermore, the core board may have been provided with plated-throughholes. In the second invention among inventions of the third group, thedifference between the thickness of the plated-through hole conductorand the thickness of the conductor circuit on the interlayer resininsulating layer is so small that an impedance alignment between the twoconductors can be more easily attained.

In the multilayer printed circuit board according to the third inventionof the third group, the thickness of the conductor circuit on the coreboard is restricted to a maximum of 10 μm in excess of the thickness ofthe conductor layer on the interlayer resin insulating layer. Since thethickness of the former is not much different from and the conductorlayer on the interlayer resin insulating layer, an impedance alignmentcan be easily attained between the conductor circuit on the core boardand the conductor layer on the interlayer resin insulating layer, withthe result that the high-frequency characteristic of the multilayerprinted circuit board can be improved.

It is preferable that the thickness of the conductor circuit on the coreboard be not greater than the conductor layer on the interlayer resininsulator layer by more than 7 μm. If the thickness difference betweenthe conductor circuit on the core board and the conductor layer on theinterlayer resin insulating layer is too large, a heat cycle-associatedstress may develop to cause cracks in the interlayer resin insulatinglayer.

The process for manufacturing a multilayer printed circuit boardaccording to the fourth invention of the third group comprises thinningthe copper foil of a copper-clad laminate by etching, pattern-etchingthe copper foil of the copper-clad laminate to provide a conductorcircuit, and, over this conductor circuit, building up an interlayerresin insulating layer and a conductor layer alternately and repeatedlyto provide a multilayer printed circuit board, wherein the thickness ofthe conductor circuit on said core board is restricted to a maximum of10 μm over the thickness of the conductor layer on the interlayer resininsulating layer.

In accordance with this production process, detailed patterning andimpedance alignment can be simultaneously accomplished.

Meanwhile, Japanese Kokai Publication Hei-2-22887 discloses a processfor manufacturing a thin copper-clad substrate board by a 25 to 90% etchof copper foil but this publication does not describe, or even suggest,the manufacture of a multilayer printed circuit board having amultilayer or structure, nor does it address to a problem of animpedance alignment between the conductor circuit on a core board and aconductor layer on an interlayer resin insulating layer, which ismentioned in this invention of the third group, thus differentiatingitself from this invention belonging to the third group.

The copper-clad laminate which can be used in the inventions of thethird group includes various prepregs such as a glass cloth-epoxy resinprepreg, a glass cloth-bismaleimide-triazine resin prepreg, a glasscloth-fluororesin prepreg or the like, each claded with copper foil. Asthe copper-clad laminate board, both a two-side copper-clad laminate anda one-side copper-clad laminate can be used and a two-side copper-cladlaminate is most preferred.

Adjustment of the thickness of copper foil is effected by etching. Thespecific technique which can be used includes chemical etching with anaqueous sulfuric acid-hydrogen peroxide solution or an aqueous solutionof ammonium persulfate, cupric chloride or ferric chloride or physicaletching such as ion beam etching.

In the inventions belonging to the third group, the etching rate ispreferably 0.001 to 10 μm/min., particularly 0.01 to 0.3 μm/min. If theetching rate is too fast, thickness control will be difficult and avariation in thickness will be large. Conversely, an excessively slowetching speed will not be practically acceptable.

The etching temperature is preferably 20 to 80° C. The etching can beeffected by whichever of spraying and dipping.

The optimum variation in the etch-reduced thickness of copper foil isnot greater than ±1.0 μm.

The thickness of said copper-clad laminate is preferably 0.5 to 1.0 mm.If the laminate is too thick, it cannot be neatly pierced, and if it istoo thin, warpage tends to take place.

The laser for use in the formation of through holes in the inventions ofthe third group is preferably a short-pulse carbon dioxide laser with anoutput of 20 to 40 mJ and a pulse duration of 10⁻⁴ to 10⁻⁸ seconds. Thenumber of shots may be 5 to 100 shots.

When plated-through holes are formed by metallizing the inner walls ofthrough holes using an electroplating, electroless plating, sputteringor vapor deposition technique, too, a filler may be filled into theplated-through holes.

The metallized inner walls of plated-through holes may be roughened.

When the inner walls of plated-through-holes are metallized, thethickness of the copper foil and the metal layer (e.g. electrolessplated metal layer) is preferably 10 to 30 μm.

As the filler, fillers comprising bisphenol F epoxy resin and inorganicparticulate fillers such as silica, alumina, etc., and those comprisingparticulate metal and particulate resin and the like can be used.

The substrate board thus formed with plated-through holes is thenprovided with a conductor circuit. The conductor circuit is formed by anetching technique.

The surface of the conductor circuit is preferably roughened forimproved adhesion.

Then, an interlayer resin insulating layer comprising insulating resinis constructed.

As the insulating resin which can be used for the formation of saidinterlayer resin insulating layer, the same resins as those mentionedfor the inventions of the first group can be used.

In the inventions of the third group, the interlayer resin insulatinglayer may comprise an adhesive for electroless plating use. The surfaceof the insulating resin layer can be roughened by, for example,incorporating a powder soluble in an acid or oxidizing agent in theheat-resistant resin in advance which is hardly soluble in the acid oroxidizing agent and dissolving the powder with the acid or oxidizingagent.

The heat-resistant resin powder mentioned above includes powders ofvarious amino resins (melamine resin, urea resin, guanamine resin,etc.), epoxy resins (the optimum resin is a bisphenol epoxy resin curedwith an amine series curing agent), bismaleimide-triazine resin andother heat-resistant resins.

Where necessary, such an adhesive for electroless plating use maybesupplemented with a cured heat-resistant resin powder, an inorganicpowder and/or a fibrous filler.

The heat-resistant resin powder mentioned above is preferably at leastone member selected from the group consisting of (1) a heat-resistantresin powder having an average particle diameter of not more than 10 μm,(2) a flocculated particle derived from heat-resistant resin particleshaving an average diameter of not more than 2 μm, (3) a mixture of aheat-resistant resin powder having an average particle diameter of 2 to10 μm and a heat-resistant resin powder having an average particlediameter of less than 2 μm, (4) a pseudo-powder comprising aheat-resistant resin powder having an average diameter of 2 to 10 μmand, as adhered to the surface thereon, at least one member selectedfrom the group consisting of a heat-resistant resin powder or inorganicpowder having an average particle diameter of not more than 2 μm, (5) amixture of a heat-resistant resin powder having an average particlediameter of more than 0.8 μm but less than 2.0 μm and a heat-resistantresin powder having an average particle diameter of 0.1 to 0.8 μm and(6) a heat-resistant powder having an average particle diameter of 0.1to 1.0 μm. This is because those powders are capable of providing themore complex roughened surface.

The interlayer resin insulating layer can be formed with openings bymeans of a laser beam or by actinic light exposure and development.

Then, a catalyst for electroless plating use, such as a Pd catalyst, isapplied and the interior of the openings for via holes is plated to formthe required via holes and, in addition, a conductor circuit is formedon the surface of the insulating resin layer. After an electrolessplated metal film is formed on the inner walls of the openings and allover the surface of the insulating resin layer, a plating resist isdisposed and electroplating is carried out, the plating resist is thenstripped off and a conductor circuit is formed by etching.

The fourth group of the present invention is concerned with a technologyfor manufacturing a multilayer printed circuit board which comprisesforming an interlayer insulating layer on a substrate board carrying abottom-layer conductor circuit, piercing openings in said interlayerinsulating layer, imparting electrical conductivity to the surface ofsaid interlayer insulating layer and inner walls of openings, filling upthe openings by electroplating to provide via holes, and then forming anupper-layer conductor circuit, wherein said electroplating is performedusing a plating solution comprising an aqueous solution containing 0.1to 1.5 mmol/L of at least one additive selected from the groupconsisting of a thiourea, a cyanide and a polyalkylene oxide and a metalion species.

In the above process for manufacturing a multilayer printed circuitboard, an aqueous solution containing 0.1 to 1.5 mmol/L of at least oneadditive selected from the group consisting of thioureas, cyanides andpolyalkylene oxides and a metal ion species is used as theelectroplating solution.

The above-mentioned additive for incorporation in the electroplatingsolution is by nature ready to be adsorbed on the surface of conductivesubstances such as metals. Therefore, the additive is deposited on thesurface of the interlayer insulating layer and the inner walls of theopenings, which have been made conductive in advance.

However, since the rate of deposition of said additive depends on therate of diffusion, the deposition does not take place at a uniform ratebut rather the additive is adhered to more readily on theconductivity-imparted surface of the interlayer insulating layer (thelands of via holes and the wiring), not adsorbing into the openings.

The deposited additive acts as a plating inhibitor to interfere with thedeposition by electroplating. Therefore, the metal ion is preferentiallyprecipitated in the openings for via holes in the course ofelectroplating, while the ion is harder to be deposited on theconductivity-imparted surface of the insulating layer. As a result,whereas the interiors of openings for via holes are filled up with themetal deposit, the thickness of the conductor circuit-forming metal filmon the surface of the insulating layer is not increased as much. Thus,the filling of openings for via holes with the plating metal and theformation of a circuit board are concurrently achieved.

As the additive mentioned above, at least one member selected from thegroup consisting of thioureas, cyanides and polyalkylene oxides can beemployed.

The thiourea mentioned above is preferably at least one compoundselected from the group consisting of thiocarbamide (which is also knowngenerally as thiourea) and isothiourea.

The cyanide mentioned above is preferably an alkali metal cyanide. Thealkali metal cyanide includes sodium cyanide and potassium cyanide.

The preferred species of said polyalkylene oxide is polyethylene glycol.

In the invention of the fourth group, those additives can be used eachindependently or in a combination of two or more species.

The concentration of said additive is 0.1 to 1.5 mmol/L.

If the amount of the additive is less than 0.1 mmol/L, the additive willnot be deposited on the inner walls of openings for via holes at all sothat the metal ion precipitates out in excess in the interior of theopenings for via holes causing an excess blister of the deposited metalfrom the openings, while the metal ion will not precipitate appreciablyon the conductor circuit. If the amount of the additive exceeds 1.5mmol/L, the additive will be deposited as much on the interior ofopenings for via holes as on the conductivity-imparted surface of theinsulating layer, with the result that the openings cannot be filled upwith the plating metal.

Particularly when a thiourea is used as the additive, its concentrationis preferably 0.3 to 0.5mmol/L, for in this range the openings for viaholes will present with a flat smooth surface.

The metal ion species to be incorporated in the electroplating solutionfor use in this invention of the fourth group includes copper ion,nickel ion, cobalt ion, tin ion and gold ion.

As the copper plating solution, an aqueous solution containing coppersulfate and sulfuric acid is preferably used. The preferred nickelplating solution is an aqueous solution containing either nickel sulfateor nickel chloride and boric acid. The cobalt plating solution ispreferably an aqueous solution containing either cobalt chloride orbasic cobalt carbonate and hypophosphorous acid. The tin platingsolution is preferably an aqueous solution of tin chloride. The goldplating solution is preferably an aqueous solution containing goldchloride or gold-potassium cyanide.

The electroplating solution mentioned above may be thickened by addingglycerin, polyethylene glycol, cellulose, chitosan or the like.Thickening results in retarded diffusion of the additive so that adefinite difference can be easily established in the deposition amountof the additive between the opening for a vial hole and the surface ofthe insulating layer and, hence, it is easier to fill up the openingsfor via holes with the plating metal.

Thus, by the process for manufacturing a multilayer printed circuitboard according to this invention of the fourth group, the filling ofvia holes and the formation of a conductor circuit can be concurrentlyaccomplished by using at least one additive selected from the groupconsisting of thiourea, cyanides and polyalkylene oxides as a platinginhibitor.

As prior art, Japanese Kokai Publication Sho-57-116799 discloses atechnology wherein electroplating and acid cleaning are performed in athiourea-containing aqueous solution of sulfuric acid. Japanese PatentPublication Sho-62-8514 discloses a technology for pattern plating witha thiourea-containing copper sulfate plating solution. In addition,Japanese Kokai Publication Sho-49-3833 discloses a process formanufacturing a multilayer circuit board wherein a selective electrolessplating is performed with thiourea.

However, none of those patent publications describe, or even suggest,the feasibility of achieving the concurrent filling of via holes and theformation of a conductor circuit by electroplating. Thus, those priorart methods are technically distinct from the invention of the fourthgroup.

The process according to this invention of the fourth group comprisesconstructing an interlayer insulating layer on a bottom-layer conductorcircuit-carrying substrate board, piercing openings in this interlayerinsulating layer, imparting electrical conductivity to the surface ofsaid interlayer insulating layer and inner walls of said openings andfinally performing electroplating.

The preferred opening for a vial hole with which the interlayerinsulating layer is to be provided has an aspect ratio, i.e. thedepth/diameter of the opening, of 1/3 to 1/1. If the aspect ratio isless than 1/3, the opening will be too large in diameter to fill up withthe plating metal. On the other hand, if the aspect ratio exceeds 1/1,the metal ions will be hard to diffuse into the openings, resulting in afailure to fill up with the plating metal.

The diameter of openings for via holes is preferably 20 to 100 μm. Thisbecause if 100 μm is exceeded, the metal ion may not be supplied in asufficient amount to fill the via holes. Conversely, if the diameter isless than 20 μm, the metal ion will not be able to diffuse well into thevia holes, thus failing to fill the holes.

The depth of the openings for via holes is preferably 10 to 100 μm. Ifthe depth is less than 10 μm, the interlayer insulation will be toothin. If it exceeds 100 μm, the metal ions will not easily diffuse andthose may not be supplied in a sufficient amount to fill up with theplating metal.

The means for imparting electrical conductivity to the surface of saidinterlayer insulating layer and the inner walls of openings includes theformation of a metal layer by electroless plating, sputtering or vapordeposition.

The metal layer mentioned above is preferably comprised of at least onemember selected from the group consisting of copper, nickel, tin andnoble metals.

The thickness of said metal layer is preferably 0.1 to 1.0 μm. If thethickness is less than 0.1 μm, electroplating may not be successfullyaccomplished. If 1 μm is exceeded, there will be cases in which thedeposited metal cannot be etched off to provide a discrete conductorcircuit.

While said electroplating is carried out using the electroplatingsolution described hereinbefore, the procedure uses the conductivityimparted board as cathode and the plating metal as anode.

The plating metal as anode may be in the form of a ball or a rod, forinstance.

The current density is preferably 0.5 to 3 A/dm². The rationale is thatat a current density of less than 0.5 A/dm², the effect of the additivecontained in the plating solution will be too weak to successfully fillthe via holes. If, conversely, the current density exceeds 3 A/dm², thesupply of the metal ion will not catch up with the deposition speed tocause an uneven electrodeposition, leading to the so-called “burntplating”.

The thickness of the conductor circuit after electroplating ispreferably 5 to 30 μm. If the conductor circuit is less than 5 μm inthickness, the etch-off of the thin conductivity-imparting layer formedfor electroplating may result in elimination of the very conductorcircuit formed. In order to form a conductor circuit over 30 μm inthickness, the thickness of the plating resist must be increased, withthe result that a fine conductor circuit pattern cannot be implemented.

Incidentally, after the plating of openings for via holes, intermittentelectroplating (constant-voltage pulse plating) can be formed in aplating solution containing the plating metal ion using the conductorcircuit-forming surface (substrate surface) as cathode and the platingmetal as anode to provide a thick conductor circuit. Theconstant-voltage pulse plating mentioned above is outstanding in theuniformity of deposited film thickness and, therefore, makes it possibleto provide conductor circuits of uniform thickness capable of impedancealignment in the final multilayer printed circuit board.

The reason why the uniformity of plating thickness can be attained bysaid intermittent electroplating is that at the edges of the substratesurface and in the vicinity of openings for via holes, where the amountof electrodeposition tends to be large, the metal deposit is melted bythe spike current flowing momentarily toward the anode and, conversely,in the center of the substrate surface and within the openings for viaholes, where the amount of electrodeposition tends to be smaller, theplating metal is caused to precipitate out by the spike current flowingmomentarily toward the cathode just as in the remaining area, with theresult that a highly uniform electrodeposition can be achieved.

Moreover, the reason why said intermittent electroplating results in anincreased crystallinity of the plated metal film is that everyinterruption of voltage application causes a diffusion of the metal ionnear the interface of the surface being plated to insure a constant ionconcentration so that a defect of the crystal lattice hardly occurs inthe electrodeposited metal film.

The process for manufacturing a multilayer printed circuit boardaccording to the invention of the fourth group is now described.

-   (1) As the substrate board, an insulating substrate board such as a    resin substrate board or a ceramic substrate board can be used.

The resin substrate board includes an insulating board prepared bylaminating prepregs made of fibrous sheets impregnated with athermosetting resin, a thermoplastic resin or a complex resin whichcomprises thermosetting resin and thermoplastic resin, or one obtainedby hot-pressing copper-clad laminate board prepared by laminating copperfoil and such preparegs in proper registration.

As the fibrous matrix sheet, glass cloth, aramid cloth or the like canbe used.

Where necessary, plated-through holes may be provided. Theplated-through holes may have been filled with a filler and/or theplated-through holes may be covered by plating, i.e. the so-called coverplating.

-   (2) On the above substrate board, a conductor wiring is formed by a    known method, then an interlayer insulating layer is constructed on    the conductor circuit-carrying substrate board, and openings for via    holes are formed in this interlayer insulating layer. The openings    in the interlayer insulating layer can be formed by exposure and    development treatment or by irradiation with laser light.

When the interlayer insulating layer of ceramic material is to be used,a ceramic green sheet is formed with openings in advance and this greensheet is laminated.

The material for the interlayer resin insulating layer includes athermosetting resin, a thermoplastic resin, or a resin available onpartial photosensitization of a thermosetting resin or a complex resincomprising such resins.

The interlayer insulating layer can be provided by coating with anuncured resin or by hot-press lamination of an uncured resin film. As analternative, an uncured resin film in which a metal layer, such ascopper foil, has been laminated on one side can be pasted. When such aresin film is used, the metal layer in the via hole-forming areas isetched off and, then, openings are formed by irradiation with laserlight.

The resin film carrying a metal layer may for example be a copper foilhaving resin.

In forming said interlayer insulating layer, an adhesive for electrolessplating can be utilized. The adhesive for electroless plating is mostpreferably a dispersion of a cured heat-resistant resin powder solublein an acid or oxidizing agent in an uncured heat-resistant resin whichis hardly soluble in the acid or oxidizing agent. Upon treatment withthe acid or oxidizing agent, the heat-resistant resin powder isdissolving and removed to leave a roughened surface comprising anchorsresembling narrow-neck pots.

As said electroless plating adhesive, particularly in regard of curedheat-resistant resin powder, the same kinds of adhesives as mentionedhereinbefore for the inventions of the first group are preferably used.This is because, with those adhesives, the more complex anchors can beproduced.

The preferred depth profile of said roughened surface is Rmax=0.1 to 20μm for insuring a good adhesion to the conductor circuit. Particularlyin the semi-additive process, the range of 0.1 to 5 μm is recommendedbecause the electroless plated metal film can then be removed withoutsacrificing the adhesion.

The heat-resistant resin which is hardly soluble in an acid or anoxidizing agent, mentioned above, is preferably “a complex resincomprising a thermosetting resin and a thermoplastic resin” or “acomplex resin comprising a photosensitive resin and a thermoplasticresin”. The former is excellent in heat resistance, while the latterenables photolithographic to form openings for via holes.

The optimum thermosetting resin is the same resin for use in theinventions of the first group.

As to the epoxy resin, the same epoxy resin as mentioned for theinventions of the first group can be used.

The thermoplastic resin mentioned above can also be the same resin asdescribed for the inventions of the first group.

The preferred blending ratio of the thermosetting resin (photosensitiveresin) to the thermoplastic resin is (thermosetting resin(photosensitiveresin) /thermoplastic resin=)95/5 to 50/50. Within this range, a highdegree of toughness can be expected without compromise in heatresistance.

The weight ratio of the above heat-resistant resin powder to the solidmatter of said heat-resistant resin matrix is preferably 5 to 50 weight%, more preferably 10 to 40 weight %.

The heat-resistant resin powder is preferably of the same type as thatmentioned for the inventions of the first group.

-   (3) Then, on this interlayer insulating layer (on the copper foil of    the copper foil having resin, if used, as well), inclusive of the    surface of openings for via holes, a metal layer is formed to obtain    conductivity by electroless plating or sputtering.-   (4) Further, a plating resist is disposed thereon. As the plating    resist, a commercial photosensitive dry film or liquid resist can be    used.

After application of the photosensitive dry film or coating with theliquid resist, exposure with ultraviolet light and development with analkaline aqueous solution are sequentially carried out.

-   (5) The substrate board treated mentioned above is then immersed in    said electroplating solution and using the electroless plated metal    layer as cathode and the plating metal as anode, direct-current    electroplating is carried out to fill up the openings for via holes    and, at the same time, form an upper-layer conductor circuit.-   (6) The plating resist is then stripped off with a strongly alkaline    aqueous solution and the electroless plated metal layer is etched    off, whereupon said upper-layer conductor circuit and via holes are    provided as a discrete pattern.

The etching solution mentioned above is an aqueous sulfuricacid/hydrogen peroxide solution, an aqueous solution of ferric chlorideor cupric chloride, or an aqueous solution of ammonium or otherpersulfate.

-   (7) Thereafter, the steps (2) to (6) are repeated where necessary    and finally solder resists and solder bumps are formed to complete    the manufacture of a multilayer printed circuit board.

The first invention of the fifth group is concerned with a multilayerprinted circuit board which comprises a buildup circuit stratumobtainable by building up interlayer resin insulating layers andconductor layers alternately, with said conductor layers beinginterconnected by via holes, as constructed on both sides of a coreboard,

wherein said via holes are formed to plug the through holes in theplated-through holes of said core board.

In the above multilayer printed circuit board, the through holes in saidplated-through holes are preferably not larger than 200 μm in diameter.

The second invention of the fifth group is concerned with a process formanufacturing a multilayer printed circuit board comprising at least thefollowing steps (1) to (4).

-   (1) A step for piercing through holes not larger than 200 μm in    diameter in a core substrate board by means of laser light.-   (2) A step for plating said through holes to prepare plated-through    holes.-   (3) A step for forming an interlayer resin insulating layer having    openings communicating with said plated-through holes on said core    board.-   (4) A step for plating said openings in said interlayer resin    insulating layer to form via holes in the manner of filling the    through holes in said plated-through holes.

In the multilayer printed circuit board according to the first inventionof the fifth group and the process for manufacturing a multilayerprinted circuit board according to the second invention of the fifthgroup, via holes are formed in the manner of filling the through holesin the plated-through holes formed in the core board and as the regionimmediately over the plated-through hole is thus allowed to function asan internal layer pad, the dead space is eliminated. Moreover, sincethere is no need for wiring the internal layer pad for the connectionfrom the plated-through hole to the via hole, the land configuration ofthe plated-through hole can be true-round. As a result, the layoutdensity of plated-through holes in the multilayer core board can beincreased, and because the wires can be consolidated at the same pacebetween the multilayer circuit stratum formed on the face side of thecore board and the multilayer circuit stratum formed on the reverseside, the number of layers can be minimized by equating the number oflayers of the upper-layer multilayer circuit stratum to the number oflayers of the lower-layer multilayer circuit stratum. Furthermore, sincethe via hole is disposed immediately over the plated-through hole, thewiring length can be decreased to increase the signal transmissionspeed.

Furthermore, when the through hole in the plated-through hole is notlarger than 200 μm in diameter, formation of a via hole in the manner offilling the through hole does not result in any remarkable increase inthe size of the via hole so that the wiring density in the interlayerresin insulating layer provided with via holes is not decreased.

In the first and second inventions of the fifth group, an adhesive forelectroless plating is preferably used as said interlayer resininsulating layer. The optimum electroless plating adhesive is adispersion of a cured heat-resistant resin powder soluble in an acid oran oxidizing agent in an uncured heat-resistant resin which is hardlysoluble in the acid or oxidizing agent.

Upon treatment with the acid or oxidizing agent, the heat-resistantresin powder is dissolved and removed to leave a roughened surface whichcomprises anchors resembling narrow-neck pots.

As said electroless plating adhesive, particularly in regard of saidcured heat-resistant resin powder, the same kinds of adhesives asmentioned before for the inventions of the first group can be used. Thisis because, with those adhesives, the more complex anchors can beproduced.

The preferred depth of said roughened surface is Rmax=0.01 to 20 μm forinsuring a good adhesion to the conductor circuit. Particularly in thesemi-additive process, the range of 0.1 to 5 μm is preferred because theelectroless plated metal film can then be removed without sacrificingthe adhesion.

The heat-resistant resin which is hardly soluble in an acid or anoxidizing agent, mentioned above, is preferably “a complex resincomprising a thermosetting resin and a thermoplastic resin” or “acomplex resin comprising a photosensitive resin and a thermoplasticresin”. The former is excellent in heat resistance, while the latterenables photolithographic formation of openings for via holes.

The optimum thermosetting resin is the same resin as mentionedhereinbefore for the inventions of the first group.

The thermoplastic resin can be the same resin as mentioned hereinbeforefor the inventions of the first group.

The preferred blending ratio of the thermosetting resin (photosensitiveresin) to the thermoplastic resin is (thermosetting resin(photosensitive resin)/thermoplastic resin)=95/5 to 50/50. Within thisrange, a high degree of toughness can be expected without compromise inheat resistance.

The weight ratio of the above heat-resistant resin powder to the solidmatter of said heat-resistant resin matrix is preferably 5 to 50 weight%, more preferably 10 to 40 weight %.

The heat-resistant resin powder is preferably of the same type as thatmentioned for the inventions of the first group.

The adhesive layer may be comprised of two layers each having adifferent composition.

As the solder resist layer added to the surface of the multilayerprinted circuit board, a variety of resins can be used. For example,bisphenol A epoxy resin, bisphenol A epoxy resin acrylate, novolac epoxyresin, and novolac epoxy resin acrylate cured with an amine seriescuring agent or an imidazole series curing agent can be mentioned.

Meanwhile, because such a solder resist layer is made of a resin havinga rigid skeleton, the layer tends to peel off. Such peeling of thesolder resist layer can be prevented by providing a reinforcing layer.

Referring to said novolac epoxy resin acrylate, the epoxy resinobtainable by reacting a phenol novolac or cresol novolac glycidyl etherwith acrylic acid or methacrylic acid, for instance, can be used.

The imidazole series curing agent mentioned above is preferably liquidat 25° C. Being a liquid, it can be uniformly blended.

The liquid imidazole series curing agent includes1-benzyl-2-methylimidazole (product designation: IB2MZ),1-cyanoethyl-2-ethyl-4-methylimidazole (product designation: 2E4MZ-CN),and 4-methyl-2-ethylimidazole (product designation: 2E4MZ).

The amount of addition of said imidazole series curing agent ispreferably 1 to 10 weight % based on the total solid matter of saidsolder resist composition. This is because, within the above range,uniform blending can be effected.

As to the pre-cure composition of said solder resist, a glycol etherseries solvent as a solvent is preferably used.

The solder resist layer formed from such a composition does not generatefree acids so that the copper pad surface is not oxidized. Moreover, therisk for health hazards is low.

The glycol ether series solvent mentioned above is a solvent having thefollowing chemical formula (3) and is preferably at least one memberselected from the group consisting of diethylene glycol dimethyl ether(DMDG) and triethylene glycol dimethyl ether (DMTG).CH₃O—(CH₂CH₂O)_(n)—CH₃ (n=1 to 5)  (3)

This is because those solvents can dissolve the initiator benzophenoneor Michler's ketone thoroughly at an elevated temperature of about 30 to50° C.

The glycol ether series solvent mentioned above is used preferably in aproportion of 10 to 70 wt. % based on the total weight of the solderresist composition.

The solder resist composition described above may be supplemented withvarious antifoams, leveling agents, thermosetting resins for improvingheat resistance and alkali resistance or imparting flexibility, and/orphotosensitive monomers for improving image resolution.

For example, the preferred leveling agent is an acrylic ester polymer.The preferred initiator includes Ciba-Geigey's Irgacure I907, and thepreferred photosensitizer includes Nippon Kayaku's DETX-S.

The solder resist composition maybe further supplemented with a dye orpigment. This is because the wiring pattern can be masked. As such adye, phthalocyanine blue is preferred.

The thermosetting resin mentioned above as an additive includesbisphenol epoxy resin. The bisphenol epoxy resin includes bisphenol Aepoxy resin and bisphenol F epoxy resin. The former is preferred whenalkali resistance is an important parameter, while the latter ispreferred when viscosity reduction is required (when coatability is animportant consideration).

The photosensitive monomer mentioned above as an additive componentincludes polyfunctional acrylic monomers. This is because suchpolyfunctional acrylic monomers contribute to improving imageresolution. As such polyfunctional acrylic monomers, Nippon Kayaku'sDPE-6A and Kyoeisha Kagaku's R-604 can be mentioned by way of example.

The viscosity of such a solder resist composition is preferably 0.5 to10 Pa·s at 25° C., more preferably 1 to 10 Pa·s. Within this viscosityrange, the composition can be easily applied with a roll coater.

The first invention among inventions of the sixth group is concernedwith a multilayer printed circuit board comprising a buildup wiringlayers obtainable by building up an interlayer resin insulating layerand a conductor layer alternately, with each conductor layers beinginterconnected by via holes, as constructed on both sides of a coreboard,

wherein lower-layer via holes are disposed immediately over theplated-through holes formed in said core substrate, with upper-layer viaholes being disposed immediately over said lower-layer via holes.

The second invention of the sixth group is concerned with a multilayerprinted circuit board comprising buildup wiring statum obtainable bybuilding up an interlayer resin insulating layer and a conductor layeralternately, with each conductor layers being interconnected by viaholes, as constructed on both sides of a core board wherein said coreboard has plated-through holes filled up with a filler and a conductorlayer covering the surface of said filler which is exposed from theplated-through holes having lower-layer via holes, with upper-layer viaholes being disposed just above said lower-layer via holes.

The third invention of the sixth group is concerned with a multilayerprinted circuit comprising a buildup wiring layers obtainable bybuilding up an interlayer resin insulating layer and a conductor layeralternately, with the conductor layers being interconnected by viaholes, as constructed on both sides of a core board, wherein lower-layervia holes are disposed to plug the through holes in the platedthrough-holes formed in said core board, with upper-layer via holesbeing disposed just above said lower-layer via holes.

In the above multilayer printed circuit boards, bumps are preferablylocated just above the plated-through holes.

Furthermore, in those multilayer printed circuit boards, the structurein which said lower-layer via holes are filled with a metal ispreferred.

Moreover, when the multilayer printed circuit boards contain no metalfiller, the recesses in said lower-layer via holes are preferably filledwith a conductive paste or resin.

In the multilayer printed circuit board according to the first inventionof the sixth group, wherein lower-layer via holes are disposed justabove plated-through holes and upper-layer via holes are disposed justabove said lower-layer via holes, the plated-through hole, lower-layervia hole and upper-layer via hole are lined up so that the wiring lengthis reduced and, hence, the signal transmissions speed is high.

The multilayer printed circuit board according to the second inventionof the sixth group is characterized in that the plated-through holes inthe core board are filled with a filler and the surface of the fillerwhich is exposed from the plated-through hole is covered with aconductor layer so that the buildup circuit is connected to theplated-through holes through contact of said conductor layer with thevia holes. Thus, as the region just above the plated-through hole isused to function as an internal layer pad, lower-layer via holes can bedisposed immediately over the plated-through holes. Moreover, as theupper-layer via hole is disposed just over the lower-layer via hole, theplated-through hole, lower-layer via hole and upper-layer via hole arelined up so that the wiring length is reduced and the signaltransmission speed is increased.

In the multilayer printed circuit board according to the first inventionof the sixth group, lower-layer via holes are disposed in the manner ofplugging the through holes of plated-through holes formed in the coreboard to connect between the lands of the plated-through holes with thevia holes. Moreover, as the upper-layer via hole is disposed immediatelyover the lower-layer via hole, the plated-through hole, lower-layer viahole and upper-layer via hole are brought into registration, with theresult that the necessary wiring length is reduced and the signaltransmission speed is increased.

Furthermore, when the lower-layer via hole is disposed immediately overthe plated-through hole, the upper-layer via hole can be disposedimmediately over said lower-layer via hole, and the bump is disposedimmediately over said plated-through hole, the plated-through hole,lower-layer via hole, upper-layer via hole and bump are arranged inperfect registry so that the wiring length is reduced and the signaltransmission speed can be increased.

In the multilayer printed circuit board according to the sixth group ofthe present invention, an electroless plating adhesive is preferablyused as the interlayer resin insulating layer. The optimum electrolessplating adhesive is a dispersion of a cured, heat-resistant resin powderwhich is soluble in acid or oxidizing agent in an uncured,heat-resistant resin matrix which is hardly soluble in acid or oxidizingagent.

Upon treatment with an acid or an oxidizing agent, the heat-resistantresin powder is dissolved and removed to leave a roughened surfacecomprising anchors resembling narrow-necked pots.

Referring to the above electroless plating adhesive, the curedheat-resistant resin powder, in particular, is preferably the samepowder as that mentioned for use in the inventions of the first group.Such a powder forms the more complex anchors.

The depth of the roughened surface is preferably Rmax =0.01 to 20 μm forinsuring good adhesion. Particularly in the semi-additive process, therange of 0.1 to 5 μm is preferred. This is because the electrolessplated metal film may be removed without adversely affecting adhesion.

The heat-resistant resin which is hardly soluble in acid or oxidizingagent mentioned above is preferably “resin complex comprising athermosetting resin and thermoplastic resin” or a“photosensitiveresin-thermoplastic resin complex”. This is because the former is highlyheat-resistant, while the latter has the advantage that openings for viaholes can be formed by photolithography.

As said thermosetting resin, the resin mentioned for use in theinventions of the first group is preferably used.

As said thermoplastic resin, the resin mentioned for use in theinventions of the first group is preferably used.

The preferred blending ratio of thermosetting resin (photosensitiveresin) to thermoplastic resin is thermosetting (photosensitiveresin)/thermoplastic resin=95/5 to 50/50. Within this range, a highdegree of toughness can be insured without compromise in heatresistance.

The mixing weight ratio of said heat-resistant resin powder is 5 to 50weight %, preferably 10 to 40 weight %, based on the solid matter of theheat-resistant resin matrix.

As the heat-resistant resin powder, the resin powder mentioned for usein the inventions of the first group is preferably used.

The adhesive layer may comprise two layers of dissimilar compositions.

As the solder resist layer to be disposed on the surface of the printedcircuit board, the same layer as mentioned for the inventions of thefifth group can be used.

BEST MODE FOR CARRYING OUT THE INVENTION

The following examples are intended to illustrate the present inventionin further detail and should by no means be construed as defining thescope of the invention.

EXAMPLE 1

FIG. 1 (a) to (g) show an exemplary process for fabricating theconductor circuit of the printed circuit board according to theinvention and FIG. 2 (a) to (e) show an exemplary process formanufacturing a multilayer printed circuit board in accordance with theinvention.

In constructing the conductor circuit on a printed circuit board, aninsulating substrate 1001 of glass cloth-epoxy resin or BT material wasused as the insulating sheet as shown in FIG. 1 (a).

Then, 35 weight parts of acrylate (25 wt. %) of cresol novolac epoxyresin (Nippon Kayaku; mol. wt. 2500), 3.15 weight parts ofphotosensitive monomer (Toa Gosei Co.; trade mark, Aronix M315), 0.5weight part of antifoam (Sun Nopco, S-65), 3.6 weight parts ofN-methylpyrrolidone (NMP), 12 weight parts of polyethersulfone (PES),and epoxy resin powders (Sanyo Kasei; Polymerpol; 1.0 μm of averageparticle diameter, 7.2 wt. Parts, and 0.5 μm of average particlediameter, 3.09 wt. parts) were mixed together, and after supply ofadditional 30 weight parts of NMP, the mixture was milled in a beadmill. Then, 2 weight parts of imidazole series curing agent (ShikokuKasei; product designation 2E4MZ-CN), 2 weight parts ofphotopolymerization initiator(Ciba-Geigy; Irgacure I-907), 0.2 weightpart of photosensitizer (Nippon Kayaku; DETX-S) and 1.5 weight parts ofNMP were added and the whole mixture was stirred to give an electrolessplating adhesive composition.

Using a roll coater, this electroless plating adhesive 1013 was coatedon the substrate and after 20 minutes of sitting horizontally, dried at60° C. for 30 minutes to provide an electroless plating adhesive layer1013 in a thickness of 35 μm.

Both sides of the wiring substrate thus prepared were irradiated forexposure at 500 mJ/cm² with a ultra-high-pressure mercury arc lamp andheated at 150° C. for 5 hours.

The substrate was then immersed in chromic acid for 19 minutes todissolve out epoxy resin particles from the surface of the adhesivelayer. By this procedure, the electroless plating adhesive layer 1013was provided with a roughened surface (FIG. 1 (b)).

Under the following conditions, a thin electroless plated copper layer1002 was constructed in a thickness of about 1 μm (FIG. 1 (c)) . Aphotosensitive dry film was then superimposed on the copper layer and aresist 1003 was formed by light exposure and development (FIG. 1 (d)).

Electroless Copper Plating Solution:

EDTA 150 g/L Copper sulfate 20 g/L HCHO 30 mL/L NaOH 40 g/Lα,α′-Bipyridyl 80 mg/L PEG 0.1 g/LElectroless Plating Conditions:

Solution temperature: at 70° C., for 30 min.

After a thick copper electrodeposit layer 1004 was thus formed (FIG. 1(e)), the resist 1003 was removed by stripping with aqueous sodiumhydroxide solution (FIG. 1 (f)). Then, using an aqueous sulfuricacid-hydrogen peroxide solution, the thin electroless plated copperlayer 1002 was etched off (FIG. 1 (g)) to provide a conductor circuit1005.

The process shown in FIG. 2 (a) to (e) is a process for establishing anelectrical connection between two or more conductor layers 1006 a, 1006b (2 layers in the drawing) which partly comprises piercing openings inthe conductor layer 1006 a by etching, forming openings for via holes1007 within said opening between 1006 a and 1006 b by laser or othermeans (FIG. 2 (b)), forming a thin electroless plated metal layer 1008within said openings 1007 (FIG. 2 (c)) and forming a thick electrolessplated metal layer 1009 (FIG. 2 (d)) to provide via holes 1010.

First, a resin-copper foil laminate 1012 comprising copper foil 1006 a,i.e. as a metal layer, and insulating resin 1011 was hot-pressed againstthe substrate sheet on which the conductor circuit 1006 b had beenformed (FIG. 2 (a)).

Then, openings for via holes were formed by etching with an aqueoussulfuric acid-hydrogen peroxide solution and the insulating resin 1011was removed by means of a carbon dioxide gas laser, for instance (FIG. 2(c)).

Then, electroless copper plating was carried out under theabove-mentioned conditions to deposit an electroless plated copper layer1008 within said openings for a via holes.

Thereafter, a plating resist 1003 was disposed and electroplating wascarried out to form via holes 1010 and an electroplated metal layer1009.

The outstanding feature of the process for manufacturing a printedcircuit board according to the first group of the present invention isthat the electroplated metal layer is formed by a constant-voltage pulseplating technique.

FIG. 3 (a) and (b) show the typical voltage and current waveforms usedin the constant-voltage pulse plating processes according to theinvention. For reference's sake, the voltage and current waveforms of PCplating are shown in FIGS. 8 (a) and (b) and the voltage and currentwaveforms of PR plating are shown in FIGS. 9 (a) and (b).

Those waveforms were observed with the SS-570S synchroscope manufacturedby IWATSU. Sony Techtonix A6303 current probe was used as current probe,Sony Techtonix A503B as current probe amplifier, and Sony TechtonixTM502AWO as power supply.

Comparison of the voltage and current waveforms shown in FIGS. 3 (a),(b), FIGS. 8 (a), (b), and FIGS. 9 (a), (b) reveals that whereas,despite a difference in the occurrence of dissolution of the anode dueto reverse electrolysis, both the PR plating technique and the PCplating technique show generally square current waveforms, the novelconstant-voltage pulse plating technique according to the firstinvention of the first group showed a current waveform such that a spikecurrent flows momentarily toward the cathode on voltage applicationwhile a spike current flows momentarily toward the anode on voltageinterruption.

A direct current source (Sansha Denki; DC AUTO Series) was used as powersupply and the voltage application and interruption were controlled byON-OFF of a relay using a digital timer.

Electroplated copper layers were built on 255 mm×340 mm substrate sheetsby depositing substantially uniform amounts of copper by 4 differentelectroplating techniques, namely direct-current plating, PC plating, PRplating and constant-voltage pulse plating techniques, using a coppersulfate plating solution containing 180 g/L of sulfuric acid and 80 g/Lof copper sulfate under the conditions respectively indicated below inTable 1 to prepare printed circuit boards. The thickness of theelectroplated copper layer of each board was measured in the central andmarginal areas of substrate and the variation in thickness of theelectroplated copper layer in the central and marginal areas of eachboard, i.e. [(maximum thickness-minimum thickness)/average thickness],was calculated to evaluate the electrodeposition uniformity.

The results of this evaluation are presented in FIG. 4 The smaller thevalue is, the higher is the uniformity of electrodeposition.

TABLE 1 Plating time Pulse condition Current Plating OFF density time ON(reverse) (A/dm²) (sec.) DC plating −1.8 A — −1.2 52 PC plating −6.0 A(1msec.) 0 A(4 msec.)  6.0 52 (ON) PR plating −1.2 A(50 msec.) +3.6 A(2msec.)  1.2 57 (ON) Constant- −0.5 V(1 msec.) 0 V(4 msec.) — 52 voltagepulse plating Power supply: DC plating: Sansha DC AUTO 1520 PC plating:Kikusui Denshi Kogyo, Bipolar PBX20-20 PR plating: Kikusui Denshi Kogyo,Bipolar PBX20-20 Constant-voltage pulse plating: Sansha DC AUTO 1520 asDC source.

OMRON solid-state relay (G3WA-D210R) was connected to the outputterminal and switched ON and OFF with OMRON digital timer (H5CL).

It can be seen from the data in FIG. 4 that, of the above-mentioned fourdifferent electroplating techniques, the constant-voltage pulse platingtechnique provides the highest electrodeposition uniformity.

Then, the electroplated copper layer formed on a stainless steel sheetby the constant-voltage pulse technique was not annealed but directlysubjected to X-ray diffraction analysis to determine its diffractionpattern. The data are plotted in FIG. 5. The half-width value was 0.25deg.

As controls, the electroplated copper layers formed by the DC, PC and PRplating techniques, respectively, were also subjected to X-raydiffraction analysis in the same manner as above. The diffractionpatterns obtained are shown in Table 2. The respective half-width valueswere 0.45 deg., 0.40 deg. and 0.30 deg.

TABLE 2 Half-width Plating process (degrees) DC plating 0.45 PC plating0.40 PR plating 0.30 Constant-voltage pulse plating 0.25

Comparison of the data given in Table 2 reveals that, of theabove-mentioned four different electroplating techniques, theconstant-voltage pulse plating technique provides the narrowesthalf-width and, hence, highest crystallinity.

It is, therefore, clear that a conductor circuit comprising anelectroplated metal layer of remarkably high crystallinity andelectrodeposition uniformity can be provided by adopting theconstant-voltage pulse plating technique in the construction of theelectroplated metal layer as an essential requisite in the process ofthe first group of invention.

The plating substrate surface area, the composition of theconstant-voltage pulse plating solution and the plating conditions arenot particularly restricted but the following can be mentioned aspreferred typical ranges.

-   -   Plating surface size: 255˜510 mm L×255˜510 mm W    -   Plating bath composition        Cu sulfate: 50 to 80 g/L, sulfuric acid: 180 to 240 g/L,        chloride ion: 40 to 50 ppm, pH<1, bath temperature: room temp.;        anode-to-cathode distance: 10 to 20 cm    -   plating conditions        Anode: oxygen-free copper, application voltage: 0.01 to 10 V,        voltage application time: ≦10 sec., preferably 0.5×10⁻³˜5×10⁻³        sec., interruption time: ≧10⁻¹² sec., preferably 1×10⁻³˜8×10⁻³        sec., voltage time/interruption time ratio=0.01 to 100.

Furthermore, since the electroplated metal layer according to theprocess of this invention is of high crystallinity and features a lowinternal residual stress, it can be used as it is to insure highlydependable circuits and connections and the annealing for decreasingstress may be omitted.

EXAMPLE 2

The following is an example of application of this invention to themanufacture of a CMOS IC chip.

An IC wafer was fabricated by the well-known MOS wafer productiontechnology, for example by the process described in LSI ProcessEngineering, pp. 22 to 23 [Published by Ohm-sha, K.K., Jun. 20, 1987][FIG. 10 a)].

The whole surface of a substrate was subjected to Cu sputtering toprovide a Cu layer 1014 in a thickness of 0.6 μm (FIG. 10 (b)). Cusputtering can be carried out using a vacuum sputtering equipment(Tokuda Seisakusho; CFS-8EP).

Then, using a spin coater, a negative photoresist (Tokyo Auka Kogyo;OMR83) was coated on the Cu layer 1014, followed by drying. Thereafter,prebaking, exposure, development and postbaking were performed insuccession to provide a plating resist 1015 (4 μm thick, L/S=20/20 μm).Then, the sheet was immersed in 10% aqueous solution of sulfuric acidfor surface activation and constant-voltage pulse copper electroplatingwas performed under the conditions described above (FIG. 10 (c)).

The plating resist 1015 was removed with aqueous sodium hydroxidesolution and the exposed copper film 1016 was dissolved and removed withaqueous sulfuric acid-hydrogen peroxide solution to provide a CMOS IC(FIG. 10 (d)).

EXAMPLE 3

A. Preparation of a Resin Composition for Forming Roughened Surface

Mixing 34 weight parts of the resin solution dissolving 25% acrylate ofa cresol novolac epoxy resin (Nippon Kayaku, mol. wt. 2500 ) indiethylene glycol dimethyl ether (DMDG), and, 2 weight parts ofimidazole curing agent (Shikoku Kasei; 2E4MZ-CN), 4 weight parts of thephotosensitive monomer caprolactone-modified tris (acryloxylethyl)isocyanurate (Toa Gosei; trade mark, Aronix M325), 2 weight parts of thephotopolymerization initiator benzophenone (Kanto Chemical), 0.2 weightpart of the photosensitizer Michler's ketone (Kanto Chemical), 10 weightparts of photosensitive monomer (Nippon Kayaku; KAYAMER PM-21), andepoxy resin powders (Sanyo Kasei, trade mark, Polymerpole; averageparticle diameter 1.0 μm, 15 weight parts and average particle diameter0.5 μm, 10 weight parts), and with addition of 30.0 weight parts ofN-methylpyrrolidone (NMP), the mixture was adjusted to a viscosity of 7Pa·s using a homodisper and further compounded with a 3-roll calender toprovide a photosensitive resin composition for forming a roughenedsurface (for an interlayer resin insulating layer).

B. A Process for Manufacturing a Printed Circuit Board

-   (1) A copper-clad laminate prepared by laminating a 18 μm-thick    copper foil 2008 to both sides of a 0.6 mm-thick substrate 2001    comprising glass epoxy resin or BT (bismaleimide triazine) was used    as a starting material (FIG. 11 (a)). First, this copper-clad    laminate was drilled, electroless plated, and pattern-etched to    provide a lower-layer conductor circuit 2004 and plated-through    holes 2009 on both sides of the substrate 2001.-   (2) The substrate board thus formed with plated-through holes 2009    and a lower-layer conductor circuit 2004 was rinsed, dried and    subjected to blackening using an aqueous solution containing NaOH    (10 g/L), NaClO₂ (40 g/L) and Na₃PO₄ (16 g/L) as blackening bath    (oxidizing bath) and a reduction treatment using an aqueous solution    containing NaOH (19 g/L) and NaBH₄ (5 g/L) as reducing bath to    provide the whole surface of the lower-layer circuit 2004 inclusive    of plated-through holes 2009 with roughened surfaces 2004 a and 2009    a (FIG. 11 (b)).-   (3) Using a roll coater, a filler 2010 containing bisphenol F epoxy    resin was coated on one side of the substrate to fill the spaces    between the lower-layer conductors 2004 or in the plated-through    holes 2009 and oven-dried. Then, the resin filler 2010 was similarly    filled up in the spaces between the conductors 2004 on the other    side or in the plated-through holes 2009 and oven-dried (FIG. 11    (c)).-   (4) One side of the substrate board which had undergone the above    procedure (3) was abraded with a belt sander using #600 belt sanding    paper (Sankyo Rikagaku) to thoroughly remove the resin filler 2010    from the surface of the inner-layer copper pattern 2004 and the    lands of the plated-through holes 2009. Then, buffing was carried    out to remove the flaws produced by the above belt-sanding. The    above series of operations was repeated for the other side of the    substrate board.

Then, the substrate board was heat-treated at 100° C. for 1 hour, 120°C. for 3 hours, 150° C. for 1 hour and 180° C. for 7 hours to cure theresin filler 2010.

Since the surface layer of the resin filler 2010 in plated-through holes2009 and non-conductor circuit-forming area and the surface of thelower-layer conductor circuit 2004 were thus flattened, the resin filler2010 was firmly bonded to the roughened lateral sides 2004 a of thelower-layer conductor circuit 2004 and also to the roughened inner wallsurfaces 2009 a of plated-through holes 2009 to provide an insulatingsubstrate board (FIG. 11 (d)).

-   (5) The above substrate board was rinsed with water, acid-degreased,    and soft-etched. Then, both sides of the substrate board are sprayed    with an etching solution to etch the surface of the lower-layer    conductor circuit 2004 and the land and inner wall surfaces of the    plated-through holes 2009, thus forming roughened surfaces 2004 a    and 2009 a over the whole surface of the lower-layer conductor    circuit 2004 (FIG. 12 (a)). The etching solution used was a mixture    of 10 weight parts of imidazole copper (II) complex, 7 weight parts    of glycolic acid, 5 weight parts of potassium chloride and 78 weight    parts of deionized water.

This substrate board was further immersed in an electroless tinsubstitution plating bath comprising a tin borofluoride (0.1mol/L)-thiourea (1.0 mol/L) solution at 50° C. for 1 hour to provide a0.3 μm-thick substitution-plated tin layer on the surface of theroughened layer. This plated metal layer is not shown in the drawing.

-   (6) Using a roll coater, the resin composition for forming roughened    surface prepared by the procedure described above in A was applied    on both sides of the substrate board which had undergone the above    treatment (5) and the coated board was allowed to sit in the    horizontal position for 20 minutes and oven-dried at 60° C. for 30    minutes to provide a 60 μm-thick resin composition for forming    roughened surface layer 2002 (FIG. 12 (b)) . Then, a polyethylene    terephthalate film was pasted to this resin composition for forming    roughened surface layer 2002 with an addhesive.-   (7) A 5 mm-thick soda-lime glass substrate printed with black    circular dots using light-screen ink was superimposed on both sides    of the substrate board 2001 treated with the resin composition for    forming roughened surface layer 2002 in (6) above, with its printed    side in intimate contact with the substrate board, and exposed to    light at 3000 mJ/cm² with an ultrahigh-pressure mercury arc lamp,    followed by spray-development with DMDG solution to provide via hole    openings 2006 having a diameter of 100 μm. Then, the substrate board    was heat-treated at 100° C. for 1 hour and 150° C. for 5 hours to    provide a 50 μm-thick interlayer resin insulating layer 2002    comprising via hole openings 2006 having a good dimensional    tolerance comparable to that of the photomask (FIG. 12 (c)). It    should be understood that, in the openings for via holes, the    roughened layer was subjected to be partially exposed.-   (8) The board formed with via hole openings 2006 was immersed in a    chromic acid-containing solution for 2 minutes to dissolve and    removed epoxy resin particles from the surface of the interlayer    resin insulating layer 2002 to roughen (to a depth of 5 μm) the    surface of the interlayer resin insulating layer 2002 and, then,    immersed in a neutralizing solution (Shiplay) and rinsed (FIG. 12    (d)).

Then, a palladium catalyst (Atotech) was applied to the roughenedsurface of the substrate board to let the catalyst nucleus be depositedon the surface of the interlayer resin insulating layer 2002 and theinner walls of the via hole openings 2006.

-   (9) Then, the substrate board was immersed in an aqueous electroless    copper plating solution of the following composition to provide a 3    μm-thick electroless plated copper film 2012 all over the roughened    surface (FIG. 13 (a)).

[Aqueous electroless plating solution] NiSO₄ 0.003 mol/L Tartaric acid0.20 mol/L Copper sulfate 0.03 mol/L HCHO 0.05 mol/L NaOH 0.10 mol/Lα,α′-Bipyridyl 40 mg/l Polyethylene glycol (PEG) 0.1 g/l [Electrolessplating conditions] Bath temperature 33° C.

The board which had undergone the above process was cut longitudinallyand the cross-section was examined under the microscope. FIG. 16 is apartially exaggerated schematic sectional view showing the thicknessprofile of the electroless plated copper film obtained.

As shown in FIG. 16, the electroless plated copper film 2012 formed inthe recesses of the roughened layer of the interlayer resin insulatinglayer 2002 is comparatively less in thickness than the electrolessplated copper film 2012 formed in the convex areas of the roughenedsurface. Therefore, the plated metal film in the concave areas can alsobe thoroughly removed in the etching stage described below.

-   (10) A commercial photosensitive dry film was bonded on the    electroless plated copper film 2012 by hot-pressing, and a 5    mm-thick soda-lime glass substrate carrying a chromium layer in a    mask pattern for non-plating resist-forming areas was placed on the    photosensitive dry film with its side carrying said chromium layer    in intimate contact with the film, followed by exposure at 100    mJ/cm² and development with 0.8% sodium carbonate to provide a 15    μm-thick plating resist 2003 (FIG. 13 (b)).-   (11) Then, copper electroplating was performed under the following    conditions to provide a 15 μm-thick electroplated copper film 2013    (FIG. 13 (c)).

[Aqueous electroplating solution] Sulfuric acid 180 g/L Copper sulfate80 g/L Additive 1 ml/L (Atotech Japan, Caparacid GL) [Electroplatingconditions] Current density 1.2 A/dm² Time 30 min. Temperature Roomtemperature

-   (12) After the plating resist 2003 was stripped with 5% KOH, the    electroless plated film 2012 beneath the plating resist 2003 was    etched off with a mixture of sulfuric acid and hydrogen peroxide to    provide a 18 μm-thick conductor circuit (inclusive of via holes    2007) 2005 comprising electroless plated copper film 2012 and    electroplated plated copper film 2013 (FIG. 13 (d)).-   (13) The above sequence of steps (5) to (12) was repeated to further    build up an interlayer resin insulating layer and a conductor    circuit to provide a multilayer printed circuit board. However, no    Sn substitution was performed (FIG. 14 (a) to FIG. 15 (b)).-   (14) Then, 46.67 weight parts of a 60 wt. % DMDG solution of a    photosensitized oligomer (mol. wt. 4000) obtained by acrylating 50%    of the epoxy groups of cresol novolac epoxy resin (Nippon Kayaku),    6.67 weight parts of a 80 weight % solution of bisphenol A epoxy    resin (Yuka Shell; trade mark, Epikote 101) in methyl ethyl ketone,    6.67 weight parts of a solution of bisphenol A epoxy resin (Yuka    Shell; Epikote E-1001-B80) in the same solvent, 1.6 weight parts of    imidazole series curing agent (Shikoku Kasei; product designation    2E4MZ-CN), 6 weight parts of photosensitive monomer (Nippon Kayaku;    KAYAMER PM-21), 0.36 weight part of polyacrylate-type leveling agent    (Kyoeisha Kagaku, trade mark, Polyflow No. 75) were taken in a    vessel and stirred and mixed to prepare a mixed composition. To this    mixed composition, 2.0. weight parts of the photopolymerization    initiator Irgacure I-907 (Ciba-Geigey), 0.2 weight part of the    photosensitizer DETX-S (Nippon Kayaku) and 0.6 weight part of DMDG    were added to provide a solder resist composition adjusted to a    viscosity of 1.4±0.3 Pa·s at 25° C.

Viscosity measurement was carried out using a Type B viscosimeter (TokyoKeiki; DVL-B) using a rotor No. 4 for 60 rpm and a rotor No. 3 for 6rpm.

-   (15) Then, both sides of the multilayered circuit board were coated    with the above solder resist composition in a thickness of 20 μm and    dried at 70° C. for 20 minutes and 70° C. for 30 minutes.    Thereafter, a 5 mm-thick soda-lime glass substrate carrying a    chromium layer in a mask pattern corresponding to solder resist    openings was placed on the solder resist layer with its side    carrying the chromium in intimate contact with the layer and UV    light exposure at 1000 mJ/cm² and development with DMTG solution    were carried out to provide openings having a diameter of 200 μm.

Then, the substrate board was further heat-treated at 80° C. for 1 hour,100° C. for 1 hour, 120° C. for 1 hour and 150° C. for 3 hours to curethe solder resist to provide a 20 μm-thick solder resist layer 2014having openings.

-   (16) Then, the substrate board formed with said solder resist layer    2014 was immersed in an electroless nickel plating solution (pH=5)    containing nickel chloride (30 g/L), sodium hypophosphite (10 g/L)    and sodium citrate (10 g/L) for 20 minutes to provide a 5 μm-thick    plated nickel layer 1015 in the openings. This board was then    immersed in an electroless plating solution containing potassium    cyanide-gold (2 g/L), ammonium chloride (75 g/L), sodium citrate (50    g/L) and sodium hypophosphite (10 g/L) at 93° C. for 23 seconds to    form a 0.03 μm-thick plated gold layer 2016 on the plated nickel    layer 2015.-   (17) Then, a solder paste was printed in the openings of the solder    resist layer 2014 and caused to reflow at 200° C. to form solder    bumps (solder masses) 2017 and, thus, provide a multilayer printed    circuit board having solder bumps 2017 (FIG. 15 (C)).

COMPARATIVE EXAMPLE 1

Using the following electroless plating solution, a multilayer printedcircuit board was fabricated in otherwise the same manner as in Example1.

[Aqueous electroless plating solution] EDTA 40 g/L Copper sulfate 10 g/LHCHO 6 ml/L NaOH 6 g/L α,α′-Bipyridyl 40 mg/L Polyethylene glycol (PEG)10 g/L

The printed circuit boards thus fabricated in Example 1 and ComparativeExample 1 were respectively allowed to sit in an environment of 121° C.,100% R.H., and 2 atmospheres for 168 hours to see whether the powersource plain conductor layer (other than the mesh pattern) would developblistering.

As regards the residual conductor between wirings, the surface wasmicroscopically examined after completion of step (12) and evaluated. Inaddition, the printed circuit board was cut along the via hole toevaluate the throwing power in the via hole region. The chromic acidremoval of the resin surface layer between the conductor circuit was notperformed.

The results of evaluation are shown below in Table 3.

TABLE 3 Throwing power Residual metal Incidence of in via hole depositbetween blistering openings conductor wirings Example 3 No blisters GoodNo residue Comparative Blisters Good Residues found Example 1 found

It will be apparent from Table 3 that the printed circuit boardaccording to Example 3 shows neither blistering nor conductor residuesand indicates a satisfactory throwing power.

EXAMPLE 4

The architecture of the multilayer printed circuit board 3010 accordingto the examples is now described with reference to FIG. 23. Themultilayer printed circuit board 3010 comprises a core board 3030,conductor circuits 3034 and 3034 formed on its face and reverse sides,respectively, and buildup circuit strata 3080A and 3080B formed oversaid conductor circuits 3034 and 3034. The buildup strata 3080A and3080B comprise an interlayer resin insulating layer 3050 formed with viaholes 3060 and a conductor circuit 3058 and an interlayer resininsulating layer 3150 formed with via holes 3160 and a conductor circuit3158, respectively.

Disposed on the top surface of the multilayer printed circuit board 3010are solder bumps 3076U for connection to the lands of IC chips (notshown). Each solder bump 3076U is connected to plated-through hole 3036through via hole 3160 and via hole 3060.

On the other hand, the underside of the printed circuit board 3010 isprovided with solder bumps 3076D for connection to the lands of daughterboards (not shown). The solder bump 3076D is connected to plated-throughhole 3036 through via hole 3160 and via hole 3060.

In the multilayer printed circuit board 3010 according to Example 4, theconductor circuit 3034 on the core board 3030 is formed in a thickness(t₃₁) of 18 μm and the conductor layers 3058 and 3158 on the interlayerresin insulating layers 3050 and 3150 are formed in a thickness (t₃₂) of18 μm. Thus, the thickness of conductor circuit 3034 is virtually notdifferent from the thickness of conductor layers 3058 and 3158, so thatan impedance alignment is insured between the conductor circuit 3034 onsaid core board 3030 and the conductor layer 3058 or 3158 on theinterlayer resin insulating layer, thus contributing to a satisfactoryhigh-frequency characteristic.

In the following, a process for the multilayer printed circuit board3010 is explained. First, the recipes for preparation of A. electrolessplating adhesive, B. interlayer resin insulating agent, C. resin filler,and D. solder resist are explained.

A. Production of Starting Compositions for the Preparation of anElectroless Plating Adhesive (Upper-Layer Adhesive)

-   (1) Resin composition {circle around (1)} was prepared by mixing and    stirring 35 weight parts of resin solution dissolving a 80 wt. %    solution of 25% acrylate of cresol novolac epoxy resin (Nippon    Kayaku; mol. wt. 2500) in DMDG, 3.15 weight parts of photosensitive    monomer (Toa Gosei; Aronix M315), 0.5 weight part of antifoam (Sun    Nopco; S-65) and 3.6 weight parts of NMP.-   (2) Resin composition {circle around (2)} was prepared by mixing 12    weight parts of polyethersulfone (PES) with epoxy resin powders    (Sanyo Kasei; Polymerpol) (7.2 weight parts of a powder having an    average particle diameter of 1.0 μm, and 3.09 weight parts of a    powder having an average particle diameter of 0.5μm), adding 30    weight parts of NMP to the mixture and agitating the whole mixture    to mix in a bead mill.-   (3) Curing agent composition {circle around (3)} was prepared by    mixing and stirring 2 weight parts of imidazole series curing agent    (Shikoku Kasei; 2E4MZ-CN), 2 weight parts of photopolymerization    initiator (Ciba-Beigy; Irgacure I-907), 0.2 weight part of    photosensitizer (Nippon Kayaku; DETX-S) and 1.5 weight parts of NMP.    B. Starting Compositions for Preparation of an Interlayer Resin    Insulating Agent (Adhesive for Lower Layer)-   (1) Resin composition {circle around (1)} was prepared by mixing and    stirring 35 weight parts of resin solution dissolving a 80 wt. %    solution of 25% acrylate of cresol novolac epoxy resin (Nippon    Kayaku; mol. et. 2500) in DMDG, 4 weight parts of photosensitive    monomer (Toa Gosei; Aronix M315), 0.5 weight part of antifoam (Sun    Nopco; S-65) and 3.6 weight parts of NMP.-   (2) Resin composition {circle around (2)} was prepared by mixing 12    weight parts of polyethersulfone (PES) with 14.49 weight parts of an    epoxy resin powder having an average particle diameter of 0.5 μm    (Sanyo Kasei; Polymerpole) and adding 30 weight parts of NMP to the    mixture, and agitating the whole mixture to mix in a bead mill.-   (3) Curing composition {circle around (3)} was prepared by mixing    and stirring 2 weight parts of imidazole series curing agent    (Shikoku Kasei; 2E4MZ-CN), 2 weight parts of photopolymerization    initiator (Ciba-Geigy; Irgacure I-907), 0.2 weight part of    photosensitizer (Nippon Kayaku, DETX-S) and 1.5 weight parts of NMP.    C. Production of Starting Compositions for Preparation of a Resin    Filler-   (1) A resin composition was prepared by mixing and stirring 100    weight parts of bisphenol F epoxy monomer (Yuka Shell; mol. wet.    310, YL983U), 170 weight parts of surface-silanated Sio₂ beads with    an average diameter of 1.6 μm (Adomatic; CRS 1101-CE; the maximum    particle size controlled below the thickness (15 μm) of the    inner-layer copper pattern to be described below) and 1.5 weight    parts of leveling agent (San Nopco; Levenol S4) and adjusting the    viscosity of the mixture to 45,000 to 49,000 cps at 23±1° C.-   (2) Imidazole series curing agent (Shikoku Kasei; 2E4MZ-CN), 6.5    weight parts.-   (3) A resin filler was prepared by mixing mixtures (1) and (2).    D. Preparation of a Solder Resist Composition

A solder resist composition was prepared by mixing 46.67 g of a 60 wt. %solution of a photosensitized oligomer (mol. wt. 4000) prepared byacrylating 50% of the epoxy groups of cresol novolac epoxy resin (NipponKayaku) in DMDG, 15.0 g of a 80 wt. % solution of bisphenol A epoxyresin (Yuka Shell; Epikote 1001) in methyl ethyl ketone, 1.6 g ofimidazole series curing agent (Shikoku Kasei; 2E4MZ-CN), 3 g ofphotosensitive polyfunctional acrylic monomer (Nippon Kayaku, R604), 1.5g of photosensitive polyfunctional acrylic monomer (Kyoeisha Chemical;DPE6A) and 0.71 g of dispersion antifoam (San Nopco; S-65), followed byaddition of 2 g of photopolymerization initiator benzophenone (KantoChemical) and 0.2 g of photosensitizer Michler's ketone (KantoChemical). The viscosity of the resulting mixture was adjusted to 2.0Pa·s at 25° C.

The process for manufacturing a multilayer printed circuit board isdescribed in the following.

-   (1) As the starting material, a copper-clad laminate 3030A    (Mitsubishi gas, HL830) laminating a 12 μm-thick copper foil 3031 to    both sides of a 0.8 mm-thick substrate 3030 having glass-epoxy resin    as shown in FIG. 17 (A) was used. Both sides of copper foil 3031    were adjusted to 3μm of thickness by using etching solution    (Mitsubishi gas, SE-07) (FIG. 17 (B)).-   (2) Through holes 3030 were pierced in the substrate 3030 by using a    drill having φ=0.3 mm. (FIG. 17 (C)). Then, the desmear treatment    was carried out in the inner surface of the substrate 3032 by using    potassium permanganate.-   (3) The whole substrate board 3030 was treated with acid catalyst,    then 0.1 μm of electroless plating layer 3035 was formed. Then, the    copper-electroplating is carried out in the current of 1 A/dm² via    said electroless plated layer 3035 to prepare the plated layer 3033    of the thickness in 15 μm (FIG. 17 (D)). As a result, plated-through    holes 3036 were formed in the through holes 3032.-   (4) The conductor circuit 3034 was formed by attaching the dry film    resist (ASAHI chemical, Co., AQ4059: not shown) to the surface of    copper-foil 3031 in the plated film 3033 to form the pattern in    L/S=50/50μm, etching with cupric chloride.

Then, the roughened layers 3038 was formed in the surface of theconductor circuit (inner layer copper pattern) 3034 and the surface andlateral sides of land 3036 a of plated-through holes 3036 (FIG. 18 (F)). The roughened layers 3038 were formed by washing the above-mentionedsubstrate 3030 with water and dried, sprayed with an etching solution toboth sides thereof, etching the surface of the conductor circuit 3034and the surface and lateral sides of land 3036 a of plated-through holes3036. The etching solution used was a mixture of 10 weight parts ofimidazole copper (II) complex, 7 weight parts of glycolic acid, 5 weightparts of potassium chloride and 78 weight parts of deionized water.

-   (5) The resin layer 3040 is formed between conductor circuits 3034    of the circuit substrate and in the plated-through holes 3036 (FIG.    18 (G)) . The resin filler C prepared in advance was applied to both    sides of circuit substrate by roll coater to filled with the filler    between conductor circuits and in the plated-through holes. The    substrate was then subjected to heat treatment at 100° C. for 1    hour, 120° C. for 3 hours, 150° C. for 1 hour and 180° C. for 7    hours to cure the resin filler.-   (6) One side of the substrate board 3030 which had undergone the    above treatment (5) was abraded with a belt sander using a #600 belt    sanding paper (Sankyo Rikagaku) to thoroughly remove any residue of    resin filler 3040 from the surface of the conductor circuit 3034 and    the surface of land 3036 a of plated-through holes 3036 and,    thereafter, buffed to get rid of flaws produced in the belt sanding    operation. The above series of operations was similarly performed on    the other side of the substrate board.

The circuit substrate 3030 thus obtained comprises resin layer 3040between conductor circuits 3034 and the resin layer 3040 is formed inthe plated through-holes. The surface of the conductor circuit 3034 andthe surface and lateral sides of land 3036 a of plated-through holes3036 are thus removed to make both sides of the substrate board flat andsmooth. The resulting circuit board features a firm bond between theresin filler 3040 and roughened surface 3038 in the lateral sides of theinner-layer conductor circuit 3034 or roughened surface 3038 lateralsides of land 3036 a of plated-through holes 3036 and between the resinfiller 3040 and the lateral sides of plated-through holes.

-   (7) A roughened layer 3042 on the surfaces of the conductor circuit    3034 having a thickness of 3μm was formed by roughing the surfaces    of the conductor circuit 3034 and the surface and lateral sides of    land 3036 a of plated-through holes 3036 (FIG. 18 (I)).

Sn substitution plating carried out on the roughened layer 3042 to formthe 0.3 μm-thick Sn layer (not shown). Said substitution plating wasCu—Sn substitution plating carried out by using 0.1 mol/L of tinborofluoride and 1.0 mol/L of thiourea at 50° C. and pH=1.2.

-   (8) Using a roll coater, the interlayer resin insulating layer (for    the lower layer) 3044 with a viscosity of 1.5 Pa·s as obtained    in (9) above was coated on both sides of the substrate 3030 obtained    above within 24 hours of preparation and the substrate board was    allowed to sit in the horizontal position for 20 minutes and dried    at 60° C. for 30 minutes (prebake). Then, the photosensitive    adhesive solution (for the upper layer) 3046 with a viscosity    adjusted to 7 Pa·s as prepared in A mentioned above was coated    within 24 hours of preparation and the substrate board was allowed    to sit in the horizontal position for 20 minutes and, then, dried    (prebaked) at 60° C. for 30 minutes to provide a 35 μm-thick    adhesive layer 3050α (FIG. 19 (J)).-   (9) A photomask film (not shown) printed with black dots having φ=85    μm (not shown) was superimposed on both sides of the substrate board    3030 formed with an adhesive layer in (8) above and exposed to light    at 50 mJ/cm² using an ultrahigh-pressure mercury arc lamp. After    spray-development with DMTG solution, the substrate 3030 was further    exposed to light at 3000 mJ/cm² with the ultrahigh-pressure mercury    arc lamp and heat-treated (postbaked) at 100° C. for 1 hour, at    120° C. for 1 hour and further at 150° C. for 3 hours, whereby a 35    μm-thick interlayer resin insulating layer (binary structure) 3050    having 85 μm φ openings (openings for via holes) 3048 with a good    dimensional tolerance-corresponding to that of the photomask film    (FIG. 19 (K)) was obtained. In the openings 3048 for via holes, the    plated tin layer (not shown) was caused to be partially exposed.-   (10) The substrate board 3030 was immersed in chromic acid for 1    minutes to dissolve and removed the epoxy resin particles from the    surface of the adhesive layer 3050 to roughen the surface of said    adhesive layer 3050 (FIG. 19 (L) ), then immersed in a neutralizing    solution (Shipley) and rinsed with water.

Then, a palladium catalyst (Atotech) was applied to the surface of thesubstrate board 3030 which had been subjected to surface roughening inthe above step to deposit the catalyst nucleus on the roughened layer ofthe surface of the electroless-plating layer 3044 and the openings forvia holes 3048.

-   (11) The board 3030 was immersed in an aqueous electroless copper    plating solution of the following formulation to provide a 1.6    μm-thick electroless plated copper film 3052 all over the surface    (FIG. 19 (M)).

[Aqueous electroless plating solution] EDTA 150 g/L Copper sulfate 820g/L HCHO 30 ml/L NaOH 40 g/L α,α′-Bipyridyl 80 mg/L PEG 0.1 g/L[Electroless plating conditions] Bath temperature 70° C., for 30 min.

-   (12) A commercial photosensitive dry film (not shown) was pasted on    the electroless plated copper film 3052 and a mask (not shown) was    placed in position. Then, the exposure at 100 mJ/cm² and development    with 0.8% sodium carbonate were carried out to provide a 15 μm-thick    plating photoresist 3054 (FIG. 20 (N)).-   (13) Then, the resist-free area was copper-electroplated under the    following conditions to construct a 15 μm-thick copper layer 3056    (FIG. 20 (O)).

[Aqueous electroplating solution] Sulfuric acid 180 g/L Copper sulfate80 g/L Additive (Atotech Japan; Kaparacid GL) 1 ml/L [Electroplatingconditions] Current density 1 A/dm² Time 30 min. Temperature Room temp.

-   (14) After the plating resist 3054 was stripped off with 5% KOH, the    electroless plated metal film 3052 underneath the plating resist was    dissolved and removed by etching with an etching solution comprising    a mixture of sulfuric acid and hydrogen peroxide to provide an 18    μm(10 to 30μm)-thick conductor circuit 3058 and via holes 3060    comprising electroless plated copper film 3052 and electroplated    copper film 3056 (FIG. 20 (P)).-   (15) Following the same procedure as described in (7), a roughened    surface 3062 comprised of Cu—Ni—P alloy was formed on the surfaces    of conductor circuit 3058 and via holes 3060 and a Sn substitution    on the surface was carried out (FIG. 21 (Q)).-   (16) The sequence of steps (8) to (14) was repeated to provide an    additional upper-layer interlayer resin insulating layer 3160, via    holes 3160 and conductor circuit 3158. Furthermore, the surface of    the via holes 3160 and conductor circuit 3158 were provided with    roughened layer 3162 to complete a multilayer buildup circuit board    (FIG. 21 (R)). In this process for formation of said additional    upper-layer conductor circuit, no Sn substitution was carried out.-   (17) Then, this multilayer buildup circuit board was provided with    solder bumps. The solder resist composition described under D. was    coated in a thickness of 45 μm on both sides of the substrate board    3030 obtained in (16) above. After the substrate board was dried at    70° C. for 20 minutes and further at 70° C. for 30 minutes, a 5    mm-thick photomask film (not shown) carrying a pattern of dots (mask    pattern) was placed in intimate contact and exposure with    ultraviolet light at 1000 mJ/cm² and development with DMTG were    carried out. Then, the substrate board was further heat-treated at    80° C. for 1 hour, at 100° C. for 1 hour, at 120° C. for 1 hour and    at 150° C. for 3 hours to provide a solder resist layer 3070    (thickness: 20 μm) having openings 3071 (opening dia. 200 μm) in the    solder pad areas (inclusive of via holes and their lands) (FIG. 21    (S)).-   (18) Then, this substrate 3030 was immersed in an electroless nickel    plating solution (pH=4.5) containing 2.31×10⁻¹ mol/L of nickel    chloride, 2.8×10 ⁻¹ mol/L of sodium hypophosphite and 1.85×10⁻¹    mol/L of sodium citrate for 20 minutes to provide a 5 μm-thick    plated nickel layer 3072 in the openings 3071. Furthermore, this    board was immersed in an electroless gold plating solution    containing 4.1×10⁻² mol/L of potassium cyanide-gold, 1.87×10⁻¹ mol/L    of ammonium chloride, 1.16×10⁻¹ mol/L of sodium citrate and 1.7×10⁻¹    mol/L of sodium hypophosphite at 80% for 7 minutes and 20 seconds to    provide a 0.03 μm plated gold layer 3074 on the plated nickel layer,    whereby the via holes 3160 and conductor circuit 3158 were provided    with solder pads 3075 (FIG. 22 (T)).-   (19) Then, the openings 3071 of the solder resist layer 3070 were    printed with a solder paste followed by reflowing at 200° C. to    provide solder bumps (solder masses) 3076U, 3076D and thereby    provide a multilayer printed circuit board 3010 (FIG. 22 (U)).

In this example, since the copper foil had thinned by etching inadvance, the total thickness of copper foil 3031 and plated layer 3033each constituting the conductor circuit 3034 becomes thinner so that thefine conductor circuit 3034 can be formed by patterned-etching mentionedabove.

EXAMPLE 5

The process for the multilayer printed circuit board 3010 according toExample 5 is now described with reference to FIG. 24.

-   (1) In this Example 5, FR-5 substrate (Matsushita Denko, R5715S) was    used as both sides-copper clad laminate board 3030A (FIG. 24 (A)).    Both sides of copper foil 3031 were adjusted to 3 μm of thickness by    using etching solution (Mitsubishi gas, SE-07) (FIG. 24 (B)).-   (2) Through holes 3032 were pierced in the substrate 3030 by using a    drill having φ=0.3 mm. (FIG. 24 (C)). Then, the desmear treatment    was carried out in the inner surface of the through-holes 3032 by    using potassium permanganate.-   (3) The whole substrate board 3030 was treated with catalyst, then    0.1 μm of electroless plating layer 3035 was formed. Then, using the    dry film resist made by Nichigo morton, Co., (NIT 225), the channel    pattern (solder resist) 3092 in L/S=30/30m was provided (FIG. 24    (D)).-   (4) The electroplating layer 3033 in thickness of 15 μm and the    solder resist layer 3094 in thickness of 3 μm were formed in    resist-free parts by using the above-mentioned electroless plating    layer 3035 as a power suply (FIG. 24 (E)).-   (5) After the plating resist 3092 was stripped off with 2% NaOH, the    conductor circuit 3034 was formed by etching the electroless plated    metal film 3035 and copper foil 3031 underneath the plating resist    3092. Then, the solder resist was removed using solder plate    stripping solution (FIG. 24 (F)).

The following steps are omitted since those are the same as Example 4mentioned above in reference with FIG. 18 to FIG. 22.

In this Example 5, the copper foil 3031 of the both side copper cladlaminate board had thinned by etching in advance.

Therefore, since the copper foil 3031 had thinned in advance when theplated layer (electroless plating layer) 3035 under the resist 3031 andthe copper foil 3031 removed by etching, the total thickness of copperfoil 3031 and plated layer 3035 becomes thinner so that the fineconductor circuit can be formed by patterned-etching mentioned above.

EXAMPLE 6

The process for the multilayer printed circuit board according toExample 6 is now described with reference to FIG. 25.

-   (1) As the starting material, a copper-clad laminate 3030A (HITACHI    Kasei Industries, EA697) laminating a 12 μm-thick copper foil 3031    to both sides of a 0.8 mm-thick substrate 3030 having glass-epoxy    resin (FIG. 25 (A)) was used. Both sides of copper foil 3031 were    adjusted to 3μm of thickness by using etching solution (Mitsubishi    gas, SE-07) (FIG. 25 (B)).-   (2) Laser was irritated to the copper-clad laminate 3030A of the    substrate board 3030 using carbon dioxide gas laser (Mitsubishi    Denki, ML605GTL) with an output of 30 mJ, a pulse duration of    52×10⁻⁶ seconds and 15 shots (FIG. 25 (C)) to form the through-holes    3032 having φ=100 μm. Then, the desmear treatment was carried out in    the lateral sides of the through-holes 3032 by potassium    permanganate.-   (3) The whole substrate board 3030 was treated with catalyst, then    0.1 μm of electroless plating layer was formed. Then, the    copper-electroplating is carried out in the current of 1 A/dm²via    said electroless plated layer to prepare the plated layer 3033 of    the thickness in 15 μm (FIG. 25 (D)) . As a result, plated-through    holes 3036 were formed in the through holes 3032.-   (4) Then, the dry film resist (ASAHI chemical Co, AQ4059, not shown)    was adhered to the surface of copper foil 3031 in the plated layer    3033 to form the pattern in L/S=50/50 μm. Then etching was curried    out with copper chloride, and the resist was stripped off with 2%    NaOH to form conductor circuit 3034 (FIG. 25 (E)). The following    steps are omitted since those are the same as Example 4 mentioned    above in reference with FIG. 18 to FIG. 22.

In this Example 6, since the copper foil 3031 had thinned in, the totalthickness of copper foil 3031 and plated layer 3033 constitutingconductor circuit 3034 becomes thinner so that the fine conductorcircuit 3034 can be formed by patterned-etching mentioned above.

Through holes can be pierced by a laser in the Example 6, though throughholes were pierced by a drill in the Examples 4 and 5. Furthermore,while the surfaces of the substrate were flattened by applying the resin3040 after the formation of conductor circuit 3034 on the core board3030 in the above Examples, a flat multilayer printed board could beobtained without flattening treatment mentioned above since theconductor circuit 3034 had thinned in advance.

EXAMPLE 7

The process for the multilayer printed circuit board according toExample 7 is now described with reference to FIG. 26. Basically, theprocess is same as Example 4, however as shown in FIG. 26 (A), conductorcircuits 3034 and plated-through holes 3036 were formed in advance, andas shown in FIG. 26 (B), the only plated-through holes 3036 werefollowed by being filled with the resin filler 3040. The printed mask(not shown) which has the openings in the parts corresponding toplated-through holes was used for filling plated-through holes 3036.Then the surface was abraded (FIG. 26 (C)) to provide the roughenedlayer 3042 comprising Cu—Ni—P on the surface of the conductor circuit asshown in FIG. 26 (D).

The roughened layer was provided by the following manner. Thus, thesubstrate board was alkali-degreased, soft-etched and further treatedwith a catalyst solution comprising palladium chloride and an organicacid to apply the Pd catalyst, and after activation of the catalyst, thesubstrate board was immersed in an electroless plating solution (pH=9)comprising copper sulfate (3.2×10⁻² mol/L), nickel sulfate (2.4×10⁻³mol/L), citric acid (5.2×10⁻² mol/L), sodium hypophosphite (2.7×10⁻¹mol/L), boric acid (5.0×10⁻¹ mol/L ) and surfactant (Nisshin Chemical,Surphile 465) (0.1 g/L) . Two minute after dipping, the substrate boardwas vibrated lengthwise and crosswise every 1 seconds to thereby provide5 μm-thick Cu—Ni—P acicular alloy roughened layer on the nickel layer onthe surfaces of the conductor circuit 3034 and of lands ofplated-through holes 3036.

Then, the interlayer resin insulating layers (for the lower layer) 3044and 3046 were formed as shown in FIG. 26 (E). Since the conductorcircuit 3034 of the core board 3034 is thin, the surface of theinterlayer resin insulating layer can be flattened without filling theresin between the conductor circuits.

EXAMPLE 8

A. Production of an Electroless Plating Adhesive

-   (1) A resin composition was prepared by mixing and stirring 35    weight parts of resin solution dissolving a 80 wt. % solution of 25%    acrylate of cresol novolac epoxy resin (Nippon Kayaku; mol.    wt. 2500) in DMDG, 3.15 weight parts of photosensitive monomer (Toa    Gosei; Aronix M315), 0.5 weight part of antifoam and 3.6 weight    parts of N-methyl pyrrolidone (NMP).-   (2) Other resin composition was prepared by mixing 12 weight parts    of polyethersulfone (PES) with epoxy resin powders (Sanyo Kasei;    Polymerpol) (7.2 weight parts of a powder having an average particle    diameter of 1.0 μm, and 3.09 weight parts of a powder having an    average particle diameter of 0.5 μm), adding 30 weight parts of NMP    to the mixture and agitating the whole mixture to mix in a bead    mill.-   (3) Another resin composition was prepared by mixing and stirring 2    weight parts of imidazole series curing agent (Shikoku Kasei;    2E4MZ-CN), 2 weight parts of photopolymerization initiator    (Ciba-Beigy; Irgacure I-907), 0.2 weight part of photosensitizer    Michler's ketone (Nippon Kayaku; DETX-S) and 1.5 weight parts of    NMP.

Then, the resin compositions prepared in (1), (2) and (3) were mixed toobtain the electroless plating adhesive.

B. Process for Production of the Multilayer Printed Circuit Board

-   (1) As the starting material, a copper-clad laminate laminating a 18    μm-thick copper foil 4008 to both sides of a 1 mm-thick substrate    4001 having glass-epoxy resin or BT (bismaleimide-triazine) resin    (FIG. 28 (a)). First, this copper-clad laminate was pierced with a    drill, then the plated resist was formed, and electroless copper    plating treatment was curried out to form plated-through holes 4009.    Further, the copper foil was pattern-etched to form the inner-layer    copper pattern in each side of the substrate (lower conductor    circuit) 4004.

The substrate thus formed with the inner-layer copper pattern 4004 wasrinsed with water and dried. Then, it was subjected to anoxidation-reduction treatment using an oxidizing (blackening) solutioncontaining NaOH (10 g/L), NaClO₂ (40 g/L) and Na₃PO₄ (6 g/L) to providesaid the whole surface of the inner-layer copper pattern 4004 with aroughened layer 4004 a and 4009 a (FIG. 28 (b))

-   (2) Using a printer, the resin filler 4010 containing epoxy resin    mainly was coated on both sides of the substrate board to fill up    the clearance between the lower conductor circuits (inner-layer    copper pattern) 4004 or in plated-through holes 4009 and oven-dried.    Thus, by this process, the resin filler 4010 was filled up the    clearance between the conductor circuits (inner-layer copper    pattern) 4004 or plated-through hole 4009 (FIG. 28 (C)).-   (3) One side of the substrate which had undergone the above    treatment (2) was abraded with a belt sander using a belt sanding    paper (Sankyo Rikagaku) to thoroughly remove any residue of resin    filler 4010 from the surface of the lower conductor circuit 4004 and    the surface of the land of the plated-through hole 4009 and,    thereafter, buffed to get rid of flaws produced in the belt sanding    operation. The above series of operations was similarly performed on    the other side of the substrate board, then the resin filler 4010    was oven-dried (FIG. 28 (d)).

As the mentioned above, the surface of resin filler 4010 filled in theplated-through holes 4009 and the roughened layer 4004 a on the lowerconductor circuit 4004 were removed and both sides of the substrateboard were flattened so that the wiring substrate was obtained, in whichthe resin filler 4010 and the lateral side of the plated-through holes4009 were adheres intimately via the roughened layer 4004 a and theinner wall of the plated-through holes and the resin filler 4010 wereadheres intimately via the roughened layer 4009 a.

-   (4) The substrate board completing the above-mentioned steps was    immersed in an electroless nickel plating solution at 90 ° C.    comprising nickel chloride (30mol/L), sodium hypophosphite (10    mol/L), and sodium citrate (0.1 g/L) to provide 1.2 μm-thick nickel    plated layer 4011 a on the surface of the conductor circuit 4004 and    the surface of the land of the plated-through hole 4009.-   (5) Further, 2 μm-thick Cu—Ni—P acicular alloy roughened layer 4011    b was formed on the surfaces of the conductor circuit 4004 and lands    of plated-through holes 4009 formed nickel plated layer 4011 a    thereon, furthermore 0.3μm-thick Sn layer was formed (FIG. 29 (a)).    However, Sn layer is not shown.

The roughened layer 4011 b was formed by the following manner. Thus, thesubstrate board was alkali-degreased, soft-etched and further treatedwith a catalyst solution comprising palladium chloride and an organicacid to apply the Pd catalyst, and after activation of the catalyst, thesubstrate board was immersed in an electroless plating solution (pH=9)comprising copper sulfate (3.2×10⁻² mol/L), nickel sulfate (2.4×10 ⁻³mol/L), citric acid (5.2×10⁻² mol/L), sodium hypophosphite (2.7×10⁻¹mol/L), boric acid (5.0×10⁻¹ mol/L) and surfactant (Nisshin Chemical,Surphile 465) (0.1 g/L). Two minute after dipping, the substrate boardwas vibrated lengthwise and crosswise every 1 seconds to thereby providethe Cu—Ni—P acicular alloy roughened layer 4011 b on nickel layer 4011 aon the surfaces of the conductor circuit 4004 and lands ofplated-through holes 4009.

-   (6) Using a roll coater, the an electroless plating adhesive as    obtained in A. mentioned above was coated on both sides of the    substrate board twice, and the substrate board was allowed to sit in    the horizontal position for 20 minutes and dried at 60° C. for 30    minutes. (FIG. 29 (b))-   (7) A photomask film printed with black dots having φ=200 μm was    superimposed on both sides of the substrate board formed with an    adhesive layer in (6) above and exposed to light at 500 mJ/cm² using    an ultrahigh-pressure mercury arc lamp and spray-development with    dimethylene grycol dimethyl ether (DMTG) solution to provide    openings for via hole 4006 having φ=85 μm on the adhesive layer.    Then, the substrate was further exposed to light at 3000 mJ/cm with    the ultrahigh-pressure mercury arc lamp and heat-treated (postbaked)    at 100° C. for 1 hour, and further at 150° C. for 5 hours, whereby a    35 μm-thick interlayer resin insulating layer 4002 having φ=35 μm    openings (openings for via holes 4006) with a good dimensional    tolerance corresponding to that of the photomask film (FIG. 29 (c))    was obtained. The aspect ratio of said openings for via holes is    0.41.-   (8) The substrate formed with openings for via holes 4006 was    immersed in chromic acid (750 g/l) at 73° C. for 20 minutes to    dissolve and removed the epoxy resin particles from the surface of    the interlayer resin insulating layer 4002 to roughen the surface,    then immersed in a neutralizing solution (Shipley) and rinsed with    water (FIG. 29 (d)).

Then, a palladium catalyst (Atotech) was applied to the surface of thesubstrate board which had been subjected to surface roughening in theabove step to deposit the catalyst nucleus on the surface of theinterlayer resin insulating layer 4002 and inner side of openings forvia holes 4006.

-   (9) Thereafter, the substrate board was immersed in an aqueous    electroless copper plating solution of the following formulation to    provide a 0.8 μm-thick electroless plated copper film 4012 all over    the surface (FIG. 30 (a)).

[Aqueous electroless plating solution] EDTA 150 g/L Copper sulfate 20g/L HCHO 30 ml/L NaOH 40 g/L α,α′-Bipyridyl 80 mg/L PEG 0.1 g/L[Electroless plating conditions] Bath temperature 70° C., for 30 min.

-   (10) A commercial photosensitive dry film was pasted on the    electroless plated copper film 4012 and with a mask placed in    position, exposure at 100 mJ/cm and development with 0.8% sodium    carbonate were carried out to provide a plating photoresist 4003    (FIG. 30 (b)).-   (11) Then, electroplating was curried out in the following condition    to form 16 μm-thick copper electroplating layer 4013 (FIG. 30 (c)).    -   a) The substrate board was immersed in the mixture containing        cleaner conditioner aqueous solution (Atotech Japan, FR, 100        g/l) and sulfuric acid at 50° C., for 5 min    -   b) Washing twice with water at 50° C.    -   C) Immersed and mixed in the 10 v/v % of aqueous solution of        sulfuric acid for 1 min.    -   d) Washing with water twice.    -   e) Immersed in an aqueous electroplating solution and the direct        current plating was curried out. Thereafter, conductor circuit        4005 and via holes 4007 having a flat upper surface (16 μm        thick, L/S=37/37 μm) comprising electroless plated copper film        4012 and copper electroplating layer 4013 were formed.

[Aqueous electroless plating solution] Sulfuric acid 220 g/L Coppersulfate 65 g/L Chloride ion 40 ppm Thiourea 0.4 mmol/L [Electrolessplating conditions] Current density 1.5 A/dm² Time 48.5 min. Temperature20° C. Cathode Copper-containing phosphorus

-   (12) Then, the substrate board was immersed in an electroless nickel    plating solution containing nickel chloride (30 g/L), sodium    hypophosphite (10 g/L) and sodium citrate (10 g/L) for 20 minutes to    provide a 1.2 μm-thick plated nickel layer 4011 a on the conductor    circuit and the land 4007 of the plated-through holes (FIG. 31 (d)).

After the plating resist 4003 was stripped off with 5% KOH, theelectroless plated metal film 4012 underneath the plating resist 4003was dissolved and removed by etching with an mixture solution ofsulfuric acid and hydrogen peroxide (FIG. 31 (a))

-   (13) Following the same procedure as described in (5), a roughened    surface 4011 b comprised of Cu—Ni—P alloy was formed on the surfaces    of conductor circuit 4005 (FIG. 31 (b)).-   (14) The sequence of steps (6) to (13) was repeated to provide an    additional upper-layer conductor circuit (FIG. 31 (c)), and then the    multilayer printed circuit board was provided by forming solder    resist layers and solder bumps.

EXAMPLE 9

The multilayer printed circuit board was obtained as the same procedureas Example 8 except the concentration of thiourea 0.3 mmol/L.

EXAMPLE 10

The multilayer printed circuit board was obtained as the same procedureas Example 8 except the concentration of thiourea 0.5 mmol/L.

EXAMPLE 11

The multilayer printed circuit board was obtained as the same procedureas Example 8 except the concentration of thiourea 0.15 mmol/L.

EXAMPLE 12

The multilayer printed circuit board was obtained as the same procedureas Example 8 except the concentration of thiourea 1.30 mmol/L.

EXAMPLE 13

The multilayer printed circuit board was obtained as the same procedureas Example 8 except 0.4 mmol/L of polyethylene grycol aqueous solutionwas used instead of thiourea.

EXAMPLE 14

The multilayer printed circuit board was obtained as the same procedureas Example 8 except 0.4 mmol/L of sodium cyanide aqueous solution wasused instead of thiourea.

COMPARATIVE EXAMPLE 2

The multilayer printed circuit board was obtained as the same procedureas Example 8 except the concentration of thiourea 0.08 mmol/L.

COMPARATIVE EXAMPLE 3

The multilayer printed circuit board was obtained as the same procedureas Example 8 except the concentration of thiourea 1.55 mmol/L.

The cross sections of the multilayer printed circuit boards obtained byExamples 8 to 14 and Comparative Examples 2 to 3 were observed by lightmicroscope, and the degree of packing, thickness of the conductorcircuit, and flatness on the via holes were observed. The results wereshown in Table 4.

TABLE 4 Degree of the Flatness of Thickness of filling in the thesurface of the conductor openings via holes circuits (μm) Example 8Complete filled Flat 16.5 Example 9 Complete filled Flat 16.5 Example 10Complete filled Flat 16.5 Example 11 Complete filled Slight convexing16.5 at the center Example 12 Complete filled Slight concaving 16.5 atthe center Example 13 Complete filled Flat 16.5 Example 14 Completefilled Flat 16.5 Compar. Complete filled Convexing Not formed Ex. 2Compar. Not filled Large 16.5 Ex. 3 concaving

As obvious from the above-mentioned Table 4, the complete packing andthe formation of the conductor circuit were accomplished at the sametime by using aqueous solution containing 0.1 to 1.5 mmol/L of additivesas a plating solution at currying out an electroplating.

Further, a flat upper surface of the via holes could be obtained bysetting the concentration of thiourea at 0.3 to 0.5 mmol/L.

EXAMPLE 15

The process for manufacturing a multilayer printed board according toExample 15 is now described with reference to the drawings.

First, the recipes for preparation of A. electroless plating adhesive,B. interlayer resin insulating material, C. resin filler, and D. solderresist for use in this process for manufacturing a multilayer printedcircuit board in accordance with Example 15 are explained below.

A. Production of Starting Compositions for the Preparation of anElectroless Plating Adhesive (Upper-Layer Adhesive).

-   [Resin Composition {circle around (1)}]

A resin composition was prepared by mixing and stirring 35 weight partsof resin solution dissolving a 80 wt. % solution of 25% acrylate ofcresol novolac epoxy resin (Nippon Kayaku; mol. wt. 2500) in DMDG, 3.15weight parts of photosensitive monomer (Toa Gosei; Aronix M315), 0.5weight part of antifoam (Sun Nopco; S-65) and 3.6 weight parts of NMP.

-   [Resin Composition {circle around (2)}]

A resin composition was prepared by mixing 12 weight parts ofpolyethersulfone (PES) with epoxy resin powders (Sanyo Kasei;Polymerpol) (7.2 weight parts of a powder having an average particlediameter of 1.0 μm, and μm 3.09 weight parts of a powder having anaverage particle diameter of 0.5), adding 30 weight parts of NMP to themixture and agitating the whole mixture to mix in a bead mill.

-   [Curing Agent Composition {circle around (3)}]

A curing composition was prepared by mixing and stirring 2 weight partsof imidazole series curing agent (Shikoku Kasei; 2E4MZ-CN), 2 weightparts of photopolymerization initiator (Ciba-Beigy; Irgacure I-907), 0.2weight part of photosensitizer (Nippon Kayaku; DETX-S) and 1.5 weightparts of NMP.

B. Starting Compositions for Preparation of an Interlayer ResinInsulating Agent (Adhesive for Lower Layer)

-   [Resin Composition {circle around (1)}]

A resin composition was prepared by mixing and stirring 35 weight partsof resin solution dissolving a 80 wt. % solution of 25% acrylate ofcresol novolac epoxy resin (Nippon Kayaku; mol. et. 2500) in DMDG, 4weight parts of photosensitive monomer (Toa Gosei; Aronix M315), 0.5weight part of antifoam (Sun Nopco; S-65) and 3.6 weight parts of NMP.

-   [Resin Composition {circle around (2)}]

A resin composition was prepared by mixing 12 weight parts ofpolyethersulfone (PES) with 14.49 weight parts of an epoxy resin powderhaving an average particle diameter of 0.5 μm (Sanyo Kasei; Polymerpole)and adding 30 weight parts of NMP to the mixture, and agitating thewhole mixture to mix in a bead mill.

-   [Curing Composition {circle around (3)}]

A curing composition was prepared by mixing and stirring 2 weight partsof imidazole series curing agent (Shikoku Kasei; 2E4MZ-CN), 2 weightparts of photopolymerization initiator (Ciba-Geigy; Irgacure I-907), 0.2weight part of photosensitizer (Nippon Kayaku, DETX-S) and 1.5 weightparts of NMP.

C. Production of Starting Compositions for Preparation of a Resin Filler

-   [Resin Composition {circle around (1)}]

A resin composition was prepared by mixing and stirring 100 weight partsof bisphenol F epoxy monomer (Yuka Shell; mol. wet. 310, YL983U), 170weight parts of surface-silanated SiO₂ beads with an average diameter of1.6 μm (Adomatic; CRS 1101-CE; the maximum particle size controlledbelow the thickness (15 μm) of the inner-layer copper pattern to bedescribed below) and 1.5 weight parts of leveling agent (San Nopco;Levenol S4) and adjusting the viscosity of the mixture to 45,000 to49,000 cps at 23±1° C.

-   [Curing Composition 2{circle around (2)}]

Imidazole series curing agent (Shikoku Kasei; 2E4MZ-CN), 6.5 weightparts.

D. Preparation of a Solder Resist Composition

A solder resist composition was prepared by mixing 46.67 g of a 60 wt. %solution of a photosensitized oligomer (mol. wt. 4000) prepared byacrylating 50% of the epoxy groups of cresol novolac epoxy resin (NipponKayaku) in DMDG, 15.0 g of a 80 wt. % solution of bisphenol A epoxyresin (Yuka Shell; Epikote 1001) in methyl ethyl ketone, 1.6 g ofimidazole series curing agent (Shikoku Kasei; 2E4MZ-CN), 3 g ofphotosensitive polyfunctional acrylic monomer (Nippon Kayaku, R604), 1.5g of photosensitive polyfunctional acrylic monomer (Kyoeisha Chemical;DPE6A) and 0.71 g of dispersion antifoam (San Nopco; S-65), followed byaddition of 2 g of photopolymerization initiator benzophenone (KantoChemical) and 0.2 g of photosensitizer Michler's ketone (KantoChemical). The viscosity of the resulting mixture was adjusted to 2.0Pa·s at 25° C.

Viscosity measurement was carried out with a Type B viscometer (TokyoKeiki, DVL-B) using a rotor No. 4 for 60 rpm and a rotor No. 3 for 6rpm.

The process for manufacturing a multilayer printed circuit boardaccording to Example 15 is now described with reference to FIGS. 32 to37. In Example 15, the multilayer printed circuit board was fabricatedby the semi-additive process.

-   (1) As the starting material, a copper-clad laminate 5030A    laminating a 18 μm-thick copper foil 5012 to both sides of a 1    mm-thick substrate 5030 having glass-epoxy resin or BT    (bismaleimide-triazine) resin as shown in FIG. 32 (A) . First, using    a laser processor, through holes 5016 for plated-through holes were    pierced in this copper-clad laminate 5030A (FIG. 32 (B)).

The laser processing equipment which can be used in this step includes acarbon dioxide gas laser equipment, a UV laser equipment and an eximerlaser equipment. The preferred diameter D of the through holes 5016 is100 to 200 μm. Among said machines, the carbon dioxide gas laserequipment, which features a high processing speed and a low-costoperation and, hence, is most suited for industrial use, is the laserprocessor of choice for the practice of the invention of the fifthgroup.

Thus, when a drill is used for piercing through holes, even the smallestdiameter D of the holes is 300 μm so that when via holes 5060 are formedin the manner of covering plated-through holes 5016 as in the exampledescribed above with reference to FIG. 36 (S), the diameter of the viahole 5060 becomes large, making it mandatory to reduce the density ofvia holes 5060 in the interlayer resin insulating layer 5050 and thewiring density of the conductor circuit 5058. In this example,therefore, the reduction in wiring density on the side of the interlayerresin insulating layer 5050 is obviated by delimiting the diameter ofthrough holes 5016 to not greater than 200 μm by using a laser. Thelower limit to hole diameter of 100 μm is set only because through holesnot greater than 100 μm in diameter can hardly be pierced even with alaser beam. While, in this example, through holes not greater than 200 gm in diameter are formed with a laser equipment, it is permissible topierce through holes as large as 300 μm in diameter by means of adrilling machine as in the prior art and form via holes so as to coverthe through holes for reducing the wiring length.

-   (2) Then, the core board 5030 was electroless plated to form a    plated metal film 5018 on the inner walls of through holes 5016    (FIG. 32 (C)).-   (3) The copper foil 5012 of the core board 5030 was then    pattern-etched to provide plated-through holes 5036 and a conductor    circuit (an inner-layer copper pattern) 5034 (FIG. 32 (D)).-   (4) The substrate board 5030 thus formed with the inner-layer copper    pattern 5034 and plated-through holes 5036 was rinsed with water and    dried. Then, it was subjected to an oxidation-reduction treatment    using an oxidizing (blackening) solution containing NaOH (10 g/L),    NaClO₂ (40 g/L) and Na₃PO₄ (6 g/L) and a reducing solution    containing NaOH (10 g/L) and NaBH₄ (6 g/L) to provide said    inner-layer copper pattern 5034 and plated-through holes 5036 with a    roughened layer 5038 (FIG. 32 (E)-   (5) The starting compositions mentioned under (C) for preparation of    a resin filler were mixed and compounded to prepare a resin filler.-   (6) Using a roll coater, the resin filler 5028 obtained in (5) above    was coated on both sides of the substrate board 5030 within 24 hours    of preparation to fill up the clearance between the conductor    circuits (inner-layer copper pattern) 5034 and conductor circuit    5034 and within the plated-through holes 5036 and dried at 70° C.    for 20 minutes. The other side of the substrate was also treated    with resin filler 5028 to fill up the clearance between the    conductor circuits 5034 and in the plated-through holes 5036,    followed by oven-drying at 70° C. for 20 minutes (FIG. 33 (F)).-   (7) One side of the substrate board 5030 which had undergone the    above treatment (6) was abraded with a belt sander using a #600 belt    sanding paper (Sankyo Rikagaku) to thoroughly remove any residue of    resin filler 5028 from the surface of the inner-layer copper pattern    5034 and the surface of the land 5036 a of the plated-through hole    5036 and, thereafter, buffed to get rid of flaws produced in the    belt sanding operation. The above series of operations was similarly    performed on the other side of the substrate board (FIG. 33 (G)).

The board was then subjected to heat treatment at 100° C. for 1 hour,120° C. for 3 hours, 150° C. for 1 hour and 180° C. for 7 hours to curethe resin filler 5028.

The surface layer of the resin filler 5028 in plated-through holes 5036and the roughened layer 5038 on the inner-layer conductor circuit 5034through the roughened layer 5038 are thus removed to make both sides ofthe substrate board 5030 flat and smooth. The resulting circuit boardfeatures a firm bond between the resin filler 5028 and the lateral sidesof the inner-layer conductor circuit 5034 and between the resin filler5028 and the inner walls of plated-through holes 5036 through saidroughened layer 5038.

Thus, in this step, the surface of the resin filler 5028 and the surfaceof the inner-layer copper pattern 5034 were made flush.

-   (8) The substrate board 5030 formed with the conductor circuit 5034    was alkali-degreased, soft-etched and further treated with a    catalyst solution comprising palladium chloride and an organic acid    to apply the Pd catalyst, and after activation of the catalyst, the    substrate board was immersed in an electroless plating solution    (pH=9) comprising 3.2×10⁻² mol/L of copper sulfate, 3.9×10⁻³ mol/L    of nickel sulfate, 5.4×10⁻² mol/L of complexing agent, 3.3×10⁻¹    mol/L of sodium hypophosphite, 5.0×10⁻¹ mol/L of boric acid and 0.1    g/L of surfactant (Nisshin Chemical, Surphile 465). One minute after    dipping, the substrate board was vibrated lengthwise and crosswise    every 4 seconds to thereby provide a Cu—Ni—P acicular alloy covering    layer and a roughened layer 5029 on the surfaces of the conductor    circuit 5034 and lands 5036 a of plated-through holes 5036 (FIG. 33    (H)).

Then, a Cu—Sn substitution reaction was carried out using 0.1 mol/L oftin borofluoride and 1.0 mol/L of thiourea at 35° C. and pH=1.2 toprovide a 0.3 μm-thick Sn layer (not shown) on the roughened layer.

-   (9) The starting compositions B. for preparation of an interlayer    resin insulating layer were mixed under stirring and adjusted to a    viscosity of 1.5 Pa·s to provide an interlayer resin insulating    agent (for the lower layer).-   (10) Then, the starting compositions A. for preparation of an    electroless plating adhesive were mixed under stirring and adjusted    to a viscosity of 7 Pa·s to provide an electroless plating adhesive    solution (for the upper layer).-   (11) Using a roll coater, the interlayer resin insulating agent (for    the lower layer) 5044 with a viscosity of 1.5 Pa·s as obtained    in (9) above was coated on both sides of the substrate obtained    in (8) above within 24 hours of preparation and the substrate board    was allowed to sit in the horizontal position for 20 minutes and    dried at 60° C. for 30 minutes (prebake) . Then, the photosensitive    adhesive solution (for the upper layer) 5046 with a viscosity    adjusted to 7 Pa·s as prepared in (10) above was coated within 24    hours of preparation and the substrate board was allowed to sit in    the horizontal position for 20 minutes and, then, dried (prebaked)    at 60° C. for 30 minutes to provide a 35 μm-thick adhesive layer    5050α (FIG. 33 (I)).-   (12) A photomask film (not shown) printed with black dots having    φ=85 μm not shown was superimposed on both sides of the substrate    board 5030 formed with an adhesive layer in (11) above and exposed    to light at 500 mJ/cm² using an ultrahigh-pressure mercury arc lamp.    After spray-development with DMTG solution, the substrate 5030 was    further exposed to light at 3000 mJ/cm² with the ultrahigh-pressure    mercury arc lamp and heat-treated (postbaked) at 100° C. for 1 hour,    at 120° C. for 1 hour and further at 150° C. for 3 hours, whereby a    35 μm-thick interlayer resin insulating layer (binary structure)    5050 having 85 μm φ openings (openings for via holes) 5048 with a    good dimensional tolerance corresponding to that of the photomask    film (FIG. 34 (J)) was obtained. In the openings 5048 for via holes,    the plated tin layer (not shown) was caused to be partially exposed.-   (13) The substrate board 5030 formed with openings 5048 was immersed    in chromic acid for 19 minutes to dissolve and removed the epoxy    resin particles from the surface of the interlayer resin insulating    layer 5050 to roughen the surface of said interlayer resin    insulating layer 5050 (FIG. 34 (K)), then immersed in a neutralizing    solution (Shipley) and rinsed with water.-   (14) Then, a palladium catalyst (Atotech) was applied to the surface    of the substrate board 5030 which had been subjected to surface    roughening in the above step (13) to deposit the catalyst nucleus on    the surface of the interlayer resin insulating layer 5050.    Thereafter, the substrate board 5030 was immersed in an aqueous    electroless copper plating solution of the following formulation to    provide a 0.6 μm-thick electroless plated copper film 5052 all over    the surface (FIG. 34 (L))

[Aqueous electroless plating solution] EDTA 150 g/L Copper sulfate 20g/L HCHO 30 ml/L NaOH 40 g/L α,α′-Bipyridyl 80 mg/L PEG 0.1 g/L[Electroless plating conditions] Bath temperature 70° C., for 30 min.

-   (15) A commercial photosensitive dry film was pasted on the    electroless plated copper film 5054 formed in the above step (14)    and with a mask placed in position, exposure at 100 mJ/cm² and    development with 0.8% sodium carbonate were carried out to provide a    15 μm-thick plating photoresist 5054 (FIG. 34 (M))-   (16) Then, the resist-free area was copper-electroplated under the    following conditions to construct a 15 μm-thick copper    electroplating layer 5056 (FIG. 34 (N))

[Aqueous electroplating solution] Sulfuric acid 180 g/L Copper sulfate80 g/L Additive (Atotech Japan; Kaparacid GL) 1 ml/L [Electroplatingconditions] Current density 1 A/dm² Time 30 min. Temperature Room temp.

-   (17) After the plating resist 5054 was stripped off with 5% KOH, the    electroless plated metal film 5052 underneath the plating resist was    dissolved and removed by etching with an etching solution comprising    a mixture of sulfuric acid and hydrogen peroxide to provide an 18    μm-thick conductor circuit 5058 and via holes 5060 comprising    electroless plated copper film 5052 and electroplated copper film    5056 (FIG. 35 (O)).-   (18) Following the same procedure as described in (8), a roughened    surface 5062 comprised of Cu—Ni—P alloy was formed on the surfaces    of conductor circuit 5058 and via holes 5060 and a Sn substitution    on the surface was carried out (FIG. 35 (P)).-   (19) The sequence of steps (9) to (17) was repeated to provide an    additional upper-layer interlayer resin insulating layer 5160, via    holes 5158 and conductor circuit 5158. Furthermore, the surface of    the via holes 5160 and conductor circuit 5158 were provided with    roughened layer 5162 to complete a multilayer buildup circuit board    (FIG. 35 (Q)). In this process for formation of said additional    upper-layer conductor circuit, no Sn substitution was carried out.-   (20) Then, this multilayer buildup circuit board was provided with    solder bumps. The solder resist composition described under (D) was    coated in a thickness of 45 μm on both sides of the substrate board    5030 obtained in (19) above. After the substrate board was dried at    70° C. for 20 minutes and further at 70° C. for 30 minutes, a 5    mm-thick photomask film(not shown) carrying a pattern of dots (mask    pattern) was placed in intimate contact and exposure with    ultraviolet light at 1000 mJ/cm² and development with DMTG were    carried out. Then, the substrate board was further heat-treated at    80° C. for 1 hour, at 100° C. for 1 hour, at 120° C. for 1 hour and    at 150° C. for 3 hours to provide a solder resist layer 5070    (thickness: 20 μm) having openings 5071 (opening dia. 200 μm) in the    solder pad areas (inclusive of via holes and their lands) (FIG. 36).-   (21) Then, this board 5030 was immersed in an electroless nickel    plating solution (pH=4.5) containing 2.31×10⁻¹ mol/L of nickel    chloride, 2.8×10⁻¹ mol/L of sodium hypophosphite and 1.85×10⁻¹ mol/L    of sodium citrate for 20 minutes to provide a 5 μm-thick plated    nickel layer 5072 in the openings 5071.

Furthermore, this board was immersed in an electroless gold platingsolution containing 4.1×10⁻² mol/L of potassium cyanide-gold, 1.87×10⁻¹mol/L of ammonium chloride, 1.16×10⁻¹ mol/L of sodium citrate and1.7×10⁻¹ mol/L of sodium hypophosphite at 80% for 7 minutes and 20seconds to provide a 0.03 μm plated gold layer 5074 on the plated nickellayer, whereby the via holes 5160 and conductor circuit 5158 wereprovided with solder pads 5075 (FIG. 36).

-   (22) Then, the openings 5071 of the solder resist layer 5070 were    printed with a solder paste followed by reflowing at 200° C. to    provide solder bumps (solder masses) 5076U, 5076D and thereby    provide a multilayer printed circuit board 5010 (FIG. 36).

Finally, as shown in FIG. 37, the bumps 5076U of the multilayer printedcircuit board 5010 were set in registration with the pads 5092 of an ICchip and caused to reflow to mount the IC chip 5092 on the multilayerprinted circuit board 5010. Furthermore, the multilayer printed circuitboard 5010 was mounted on a daughter board 5094 by setting it inregistration with its pads 5096 and reflowing.

In the above-mentioned example, the multilayer printed circuit board wasfabricated by the semi-additive process, however the multilayer printedcircuit board abricated by the full additive process can be said tobelong to the fifth group of the invention.

EXAMPLE 16

In the following, the process for manufacturing a multilayer printedboard according to Example 16 is now described with reference to thedrawings.

A. Production of Starting Compositions for the Preparation of anElectroless Plating Adhesive (Upper-Layer Adhesive)

The objective compositions were obtained by the same method as Example15.

B. Starting Compositions for Preparation of an Interlayer ResinInsulating Agent (Adhesive for Lower Layer)

The objective compositions were obtained by the same method as Example15.

C. Production of Starting Compositions for Preparation of a Resin Filler

The objective compositions were obtained by the same method as Example15.

D. Preparation of a Solder Resist Composition

The objective compositions were obtained by the same method as Example15.

The process for manufacturing a multilayer printed circuit boardaccording to Example 16 is now described with reference to FIGS. 39 to45. In Example 16, the multilayer printed circuit board was fabricatedby the semi-additive process.

-   (1) As the starting material, a copper-clad laminate 6030A    laminating a 18 μm-thick copper foil 6012 to both sides of a 0.5    mm-thick substrate 6030 having glass-epoxy resin or BT    (bismaleimide-triazine) resin (FIG. 39 (A)) . Etching resists were    formed at the both sides thereof, etching treatment was curried out    with an aqueous solution of sulfuric acid-hydrogen peroxide to    provide the core board 6030 containing the conductor circuit 6014    (FIG. 39 (B)).

The core board 6030 was prepared by laminating preparegs. For example,the prepregs at B stage prepared by immersing epoxy resin, polyimideresin, bismaleimide-triazine resin, fluorine resin(polytetrafluoroethylene, etc.) were laminated to the fibrous matrixsheet or non-woven fabrics of glass cloth or aramid cloth, and thenhot-pressed to provide the core board. As the circuit board on the coreboard, there can be mentioned not shown).

The fabricating method is described in the following. Thus, thesubstrate board 6030 was acid-degreased, soft-etched and further treatedwith a catalyst solution comprising palladium chloride and an organicacid to precipitate the Pd catalyst, and after activation of thecatalyst, the substrate board was immersed in an electroless platingsolution (pH=9) comprising copper sulfate (8 g/L), nickel sulfate (0.6g/L), citric acid (15 g/L), sodium hypophosphite (29 g/L), boric acid(31 g/L ) and surfactant (0.1 g/L) to thereby provide Cu—Ni—P acicularalloy covering layer and roughened layer 6027 on the surfaces ofconductor layer 6026 covering the conductor circuit 6014 a and thefiller 6022.

Cu—Sn substitution plating was carried out by using 0.1 mol/L of tinborofluoride and 1.0 mol/L of thiourea at 50° C. and pH=1.2 to provide0.3μm-thick Sn layer (not shown) on the surface of the roughen layer6010.

The roughen layer comprised of Cu—Ni—P alloy may be also formed byforming so-called blacken-reduction layer on the surface of theconductor layer 6026 a covering the conductor circuit 6014 a and thefiller 6022, filling the resin such as bisphenol F type epoxy resinbetween the conductor circuits, abrading the surface, and plating of theabove-mentioned (9).

-   (10) The above-mentioned resin filler C. for flattening the surface    of the substrate was prepared.-   (11) Using a roll coater, the resin composition 6028 prepared by the    procedure described above in (10) was applied on both sides of the    substrate board 6030 to fill the upper conducotor layer 6026 a, to    fill the lower conducotor layer 6026 a or conductor circuit 6014 a    with the resin filler, and oven-dried at 70° C. for 20 minutes (FIG.    41 (M)).-   (12) One side of the substrate board which had undergone the above    procedure (11) was abraded with a belt sander using #600 belt    sanding paper (Sankyo Rikagaku) to thoroughly remove the resin    filler 6028 from the surface of the conducotor layer 6026 a g/L) and    NaBH₄ (6 g/L) to provide the roughened layer 6020 on the whole    surface of the conductor 6018 containing the plated-through holes    6036 (FIG. 39 (E)). Said roughened layer was formed by an    oxidation-reduction treatment, however the spray treatment with a    aqueous mixture solution containing a cupric complex compound and an    organic acid and metal plating using Cu—Ni—P alloy can be also used.-   (4) The plated-through holes 6036 were filled with the resin filler    6022 containing copper particle of average diameter=10 μm (Tatsuta    Densen, non-conductive hole-plugging copper paste, trade name; DD    paste) by screen printing, and then died and cured. (FIG. 39 (E)).    Thus, the resin filler was coated by printing method on the    substrate board set the mask on the openings of the plated-through    holes to fill the plated-through holes, and then dried and cured.

The resin filler filled in the plated-through holes comprises metalparticle, thermosetting resin and curing agent, or preferably comprisesmetal particle and thermosetting resin and, where necessary, additionalsolvents. Since, if these filler contain metal particles, the metalparticles are exposed when abrading those surface and the surface isunified with the conductor circuit formed thereon via the exposed metalparticles, stripping between the conductor layer is hardly occurred evenunder the hard condition of high temperature and high humidity such asPCT (Pressure cooker test) . These filler do not occur the migration ofmetal ion since those are filled in the plated-through holes having thewall side of metal layer.

As the metal particles, there can be used copper, gold, silver,aluminum, nickel, titanium, chromium, tin/lead, platinum. The particlediameter of those metal particles is preferably 0.1 to 50 μm. This isbecause, the surface of copper is oxidized to worsen wettability againstthe resin when the diameter is less than 0.1 μm, while the printingefficiency becomes worse when the diameter is over 50 μm. The additionamount of the metal particles is preferably 30 to 90 wt. %. This isbecause the adhesion of cover plating becomes worse when the amount isless than 30 wt. %, while the printing efficiency becomes worse when theamount is over 90 wt. %.

As the resins which can be used, epoxy resin such as bisphenol A typeand bisphenol F type, phenolic resin, polyimide resin,polytetrafluoroethylene (PTFE), bismaleimide-triazine (BT) resin, PFA,PPS, PEN, PES, nylon, alamide, PEEK, PEKK and PET can be used.

As the curing agents, imidazole type, phenol type, amine type can beused.

As the solvents, there can be mentioned NMP (normal methyl pyrrolidone)DMDG (diethylene glycol dimethyl ether), glycerin, water,1-cicrohexanol, 2-cicrohexanol, 3-cicrohexanol, cicrohexanon, methylcellsolve, methyl cellsolve acetate, methanol, ethanol, butanol,propanol.

The non-conductive filler is preferably used. This is because theshrinkage caused by curing becomes small and the stripping between theconductor layer and via holes is hardly occurred when using thenon-conductive filler.

The metal surface-improving agents such as silane coupling agents may beused for improving the bond strength between the metal particle andresin. As other additives which can be used, antiforming agents such asacryl type antiforming agent and silicone type antiforming agent,inorganic fillers such as silica, alumina, talc maybe added. Silanecoupling agents may be also coated on the surface of the metal particle.

Such fillers are printed in the following condition, for example. Thus,using mask board of mesh board made of tetron and angle squeege with 45°of angle, the printing is curried out under the condition of a Cu pasteviscosity of 120 Pa·s, squeege speed at 13 mm/sec., and squeegedepression of 1 mm.

Then, the residue of resin filler 6022 was removed from the surface ofthe roughened layer 6020 on the conductor 6018 and the plated-throughholes 6036 using a #600 belt sanding paper (Sankyo Rikagaku) and,thereafter, buffed to get rid of flaws produced in the belt sandingoperation to make the surface of the substrate board 6030 flat (FIG. 40(G)). Thus, in this step, the substrate board 6030 which comprises beingstrongly interconnected between the inner-layer of the plated-throughhole 6036 and the resin filler 6022 through the roughened layer 6020 wasprovided.

-   (5) The Pd catalyst (Atotech) was applied to the surface of the    substrate board 6030 made flattened in the above-mentioned (4), the    electroless copper plating according to the above-mentioned (2) was    curried out to provide 0.6 μm-thick electroles copper plating layer    6023 (FIG. 40 (H)).-   (6) Then, the copper-electroplating under the following conditions    was curried out to construct a 15 μm-thick copper layer 6024, thick    plating of the conductor circuit 6014, and conductor layer 6026 a    covering the filler 6022 filled in the plated-through holes 6036    (round lands of plated-through holes) (FIG. 40 (I)).

[Aqueous electroplating solution] Sulfuric acid 180 g/L Copper sulfate80 g/L Additive (Atotech Japan; Kaparacid GL) 1 ml/L [Electroplatingconditions] Current density 1 A/dm² Time 30 min. Temperature Room temp.

-   (7) A commercial photosensitive dry film was pasted on the both    sides of the substrate board 6030 forming the part of the conductor    circuit 6014 and the conductor layer 6026 a and with a mask placed    in position, exposure at 100 mJ/cm²and development with 0.8% sodium    carbonate were carried out to provide a 15 μm-thick etching resist    6025 (FIG. 40 (J)).-   (8) After the plating layers 6023, 6024 not having the etching    resist 6025 were dissolved and removed by etching with mixture of    sulfuric acid and hydrogen peroxide, and then the etching resist    6008 was stripped off with 5% KOH to provide the conductor layer    6026 a covering the isolated conductor circuit 6014 a and filler    6022 (FIG. 41 (K)).-   (9) A 2.5 μm-thick roughened layer (unevenness layer) 6027 comprised    of Cu—Ni—P alloy was formed on the surfaces of conductor circuit    6026 a covering the isolated conductor circuit 6014 a and filler    6022 and a 0.3 μm-thick Sn layer on the surface of the roughened    layer was formed (FIG. 41 (L), but Sn layer was not shown).

The fabricating method is described in the following. Thus, thesubstrate board 6030 was acid-degreased, soft-etched and further treatedwith a catalyst solution comprising palladium chloride and an organicacid to apply the Pd catalyst, and after activation of the catalyst, thesubstrate board was immersed in an electroless plating solution (pH=9)comprising copper sulfate (8 g/L), nickel sulfate (0.6 g/L), citric acid(15 g/L), sodium hypophosphite (29 g/L), boric acid (31 g/L andsurfactant (0.1 g/L) to thereby provide Cu—Ni—P acicular alloy coveringlayer and roughened layer 6027 on the surfaces of conductor layer 6026covering the conductor circuit 6014 a and the filler 6022.

Cu—Sn substitution plating was carried out by using 0.1 mol/L of tinborofluoride and 1.0 mol/L of thiourea at 50° C. and pH=1.2 to provide0.3μm-thick Sn layer (not shown) on the surface of the roughened layer6010.

The roughened layer comprised of Cu—Ni—P alloy may be also formed byforming so-called blacken-reduction layer on the surface of theconductor layer 6026 a covering the conductor circuit 6014 a and thefiller 6022, filling the resin such as bisphenol F type epoxy resinbetween the conductor circuits, abrading the surface, and plating of theabove-mentioned (9).

-   (10) The above-mentioned resin filler C. for flattening the surface    of the substrate was prepared.-   (11) Using a roll coater, the resin composition 6028 prepared by the    procedure described above in (10) was applied on both sides of the    substrate board 6030 to fill the upper conducotor layer 6026 a, to    fill the lower conducotor layer 6026 a or conductor circuit 6014 a    with the resin filler, and to be dried at 70° C. for 20 minutes    (FIG. 41 (M)).-   (12) One side of the substrate board which had undergone the above    procedure (11) was abraded with a belt sander using #600 belt    sanding paper (Sankyo Rikagaku) to thoroughly remove the resin    filler 6028 from the surface of the conducotor layer 6026 a and the    conductor circuit 6014 a. Then, buffing was carried out to remove    the flaws produced by the above belt-sanding (FIG. 41 (N)).

Then, the substrate board was heat-treated at 100° C. for 1 hour, 120°C. for 3 hours, 150° C. for 1 hour and 180° C. for 7 hours to cure theresin filler 6028.

Since the roughened layer 6027 on the surface of the conductor layer6026 a and conductor circuit 6014 a was removed and both sides of thesurface was flattened, and then the resin filler 6028, the conductorlayer 6026 a and the lateral sides of the conductor circuit 6014 a werefirmly bonded via the roughened layer 5038.

-   (13) The substrate board 6030 formed with the conductor circuit 6026    a and conductor circuit 6014 a which were exposed by the    treatment (12) mentioned above was alkali-degreased, soft-etched and    further treated with a catalyst solution comprising palladium    chloride and an organic acid to apply the Pd catalyst, and after    activation of the catalyst, the substrate board was immersed in an    electroless plating solution (pH=9) comprising 3.2×10⁻² mol/L of    copper sulfate, 3.9×10⁻³ mol/L of nickel sulfate, 5.4×10⁻² mol/L of    complexing agent, 3.3×10⁻¹ mol/L of sodium hypophosphite, 5.0×10⁻¹    mol/L of boric acid and 0.1 g/L of surfactant (Nisshin Chemical,    Surphile 465). One minute after dipping, the substrate board was    vibrated lengthwise and crosswise every 4 seconds to thereby provide    a Cu—Ni—P acicular alloy covering layer and a roughened layer 6029    on the surfaces of the conductor layer 6026 a and the conductor    circuit 6014a (FIG. 41 (O)).

Then, a Cu—Sn substitution reaction was carried out using 0.1 mol/L oftin borofluoride and 1.0 mol/L of thiourea at 35° C. and pH=1.2 toprovide a 0.3 μm-thick Sn layer (not shown) on the roughened layer.

-   (14) The interlayer resin insulating agent (adhesive for lower    layer) was prepared by mixing and stirring the composition of the    The interlayer resin insulating agent B. and adjusting the viscosity    of 1.5 Pa·s.-   (15) The electroless plating adhesive (upper-layer adhesive) was    prepared by mixing and stirring the composition of the electroless    plating adhesive A. and adjusting the viscosity of 7 Pa·s.-   (16) Using a roll coater, the interlayer resin insulating agent (for    the lower layer) 6044 with a viscosity of 1.5 Pa·s as obtained    in (14) above was coated on both sides of the substrate of the    above-mentioned (13) obtained above within 24 hours of preparation    and the substrate board was allowed to sit in the horizontal    position for 20 minutes and dried at 60° C. for 30 minutes    (prebake). Then, the photosensitive adhesive solution (for the upper    layer) 6046 with a viscosity adjusted to 7 Pa·s as prepared in (15)    mentioned above was coated within 24 hours of preparation and the    substrate board was allowed to sit in the horizontal position for 20    minutes and, then, dried (prebaked) at 60° C. for 30 minutes to    provide a 35 μm-thick adhesive layer 6050 a (FIG. 42 (P)).-   (17) A photomask film (not shown) printed with black dots having    φ=85 μm (not shown) was superimposed on both sides of the substrate    board 6030 formed with an adhesive layer in (16) above and exposed    to light at 500 mJ/cm² using an ultrahigh-pressure mercury arc lamp.    After spray-development with DMTG solution, the substrate 6030 was    further exposed to light at 3000 mJ/cm² with the ultrahigh-pressure    mercury arc lamp and heat-treated (postbaked) at 100° C. for 1 hour,    at 120° C. for 1 hour and further at 150° C. for 3 hours, whereby a    35 μm-thick interlayer resin insulating layer (binary structure)    6050 having 85 μm φ openings (openings for via holes) 6048 with a    good dimensional tolerance corresponding to that of the photomask    film (FIG. 42 (Q)) was obtained. In the openings 6048 for via holes,    the plated tin layer (not shown) was caused to be partially exposed.-   (18) The substrate board 6030 was immersed in chromic acid for 19    minutes to dissolve and removed the epoxy resin particles from the    surface of the interlayer resin insulating layer 6050 to roughen the    surface of said interlayer resin insulating layer 6050 (FIG. 42    (R)), then immersed in a neutralizing solution (Shipley) and rinsed    with water.-   (19) A palladium catalyst (Atotech) was applied to the surface of    the substrate board 6030 which had been subjected to surface    roughening in the above step to deposit the catalyst nucleus on the    surface of the interlayer resin insulating layer 6050. Then, the    substrate board 6030 was immersed in an aqueous electroless copper    plating solution of the following formulation to provide a 0.6    μm-thick electroless plated copper film 6052 all over the surface    (FIG. 42 (S)).

[Aqueous electroless plating solution] EDTA 150 g/L Copper sulfate 20g/L HCHO 30 ml/L NaOH 40 g/L α,α′-Bipyridyl 80 mg/L PEG 0.1 g/L[Electroless plating conditions] Bath temperature 70° C., for 30 min.

-   (20) A commercial photosensitive dry film (not shown) was pasted on    the electroless plated copper film 6052 prepared in the    above-mentioned (19) and a mask (not shown) was placed in position.    Then, the exposure at 100 mJ/cm² and development with 0.8% sodium    carbonate were carried out to provide a 15 μm-thick plating    photoresist 6054 (FIG. 42 (T)).-   (21) Then, the resist-free area was copper-electroplated under the    following conditions to construct a 15 μm-thick copper layer 6056    filling the openings 6048 (FIG. 43 (U)).

[Aqueous electroplating solution] Sulfuric acid 180 g/L Copper sulfate80 g/L Additive (Atotech Japan; Kaparacid GL) 1 ml/L [Electroplatingconditions] Current density 1 A/dm² Time 30 min. Temperature Room temp.

-   (22) After the plating resist 6054 was stripped off with 5% KOH, the    electroless plated metal film 6052 underneath the plating resist was    dissolved and removed by etching with an etching solution comprising    a mixture of sulfuric acid and hydrogen peroxide to provide an 18    μm-thick conductor circuit 6058 and via holes 6060 comprising    electroless plated copper film 6052 and electroplated copper film    6056 (FIG. 43 (V)).-   (23) Following the same procedure as described in (13), a roughened    surface 6062 comprised of Cu—Ni—P alloy was formed on the surfaces    of conductor circuit 6058 and via holes 6060 and a Sn substitution    on the surface was carried out (FIG. 43 (W)).-   (24) The sequence of steps (14) to (22) was repeated to provide an    additional upper-layer interlayer resin insulating layer 6150, via    holes 6160 and conductor circuit 6158. Furthermore, the surface of    the via holes 6160 and conductor circuit 6158 were provided with    roughened layer 6162 to complete a multilayer buildup circuit board    (FIG. 43 (X)). In this process for formation of said additional    upper-layer conductor circuit, no Sn substitution was carried out.    In this example, a flat multilayer buildup circuit board could be    obtained because the via holes 6060 and 6160 were formed in the    filled-via structure.-   (25) Then, this multilayer buildup circuit board was provided with    solder bumps. The solder resist composition described under D. was    coated in a thickness of 45 μm on both sides of the substrate board    6030 obtained in (24) above. After the substrate board was dried at    70° C. for 20 minutes and further at 70° C. for 30 minutes, a 5    mm-thick photomask film (not shown) carrying a pattern of dots (mask    pattern) was placed in intimate contact and exposure with    ultraviolet light at 1000 mJ/cm² and development with DMTG were    carried out. Then, the substrate board was further heat-treated at    80° C. for 1 hour, at 100° C. for 1 hour, at 120° C. for 1 hour and    at 150° C. for 3 hours to provide a solder resist layer 6070    (thickness: 20 μm) having openings 6071 (opening dia. 200 μm) in the    solder pad areas (inclusive of via holes and their lands) (FIG.    44)).-   (26) Then, this substrate 6030 was immersed in an electroless nickel    plating solution (pH=4.5) containing 2.3×10⁻¹ mol/L of nickel    chloride, 2.8×10⁻¹ mol/L of sodium hypophosphite and 1.85×10⁻¹ mol/L    of sodium citrate for 20 minutes to provide a 5 μm-thick plated    nickel layer 6072 in the openings 6071. Furthermore, this board was    immersed in an electroless gold plating solution containing 4.1×10⁻²    mol/L of potassium cyanide-gold, 1.87×10⁻¹ mol/L of ammonium    chloride, 1.16×10 ⁻¹ mol/L of sodium citrate and 1.7×10⁻¹ mol/L of    sodium hypophosphite at 80% for 7 minutes and 20 seconds to provide    a 0.03 μm plated gold layer 6074 on the plated nickel layer, whereby    the via holes 6160 and conductor circuit 6158 were provided with    solder pads 6075 (FIG. 44).-   (27) Then, the openings 6071 of the solder resist layer 6070 were    printed with a solder paste followed by reflowing at 2000C to    provide solder bumps (solder masses) 6076U, 6076D and thereby    provide a multilayer printed circuit board 6010 (FIG. 44).

Finally, as shown in FIG. 45, the bumps 6076U of the multilayer printedcircuit board 6010 were set in registration with the pads 6092 of an ICchip and caused to reflow to mount the IC chip 6092 on the multilayerprinted circuit board 6010. Furthermore, the multilayer printed circuitboard 6010 was mounted on a daughter board 6094 by setting it inregistration with its pads 6096 and reflowing.

Although, in Example 16, via holes 6060 filled with metal were providedby depositing an electroplated conductor 6056 on the electroless platedmetal layer 6052 in the openings 6048, an electroless plated metal layermay be substituted for said electroplated conductor layer 6056. In thiscase, an electroless plating resist is disposed without prior formationof an electroless plated metal layer 6052 and in the resist-free areas,via holes of the filled-via type are formed by electroless plating.

Furthermore, it is possible to fill up the openings 6048 by electrolessplating without disposing said electroless plated metal film 6052. Thus,the interlayer resin insulating layer 6050 having openings 6048communicating with the lower-layer conductor layer 6026 a can beelectroless-plated to fill up the openings 6048 without application ofan electroless plating catalyst. Since the pretreatment with anelectroless plating catalyst is not performed in this case, theelectroless plating metal is selectively deposited on the conductorlayer 6026 a in the bottom of the openings 6048. Therefore, the surfaceof this electroless plated conductor can be flat and smooth. It is alsopossible to form via holes 6060 by depositing an electroplatingconductor on this electroless plated conductor having a flat surface.

EXAMPLE 17

The process for the multilayer printed circuit board according toExample 17 is now described with reference to FIG. 46.

As to the multilayer printed circuit board according to Example 16, thecovering plated layer (the conductor layer) 6026 a was formed on theplated-through holes 6036 and the plated-through holes 6036 and viaholes 6060 were interconnected via said conductor layer 6026 a. On theother hand, as to the multilayer printed circuit board according toExample 17, via holes 6060 formed the through holes 6016 constitutingthe plated-through holes 6036 with the small diameter (100 to 200 μm) bylaser were deposited at the position covering the through holes 6016constituting the plated-through holes 6036, and lands 6036 a in theplated-through holes 6036 and via holes 6060 were electro-connected.

The laser processing equipment which can be used in this step includes acarbon dioxide gas laser equipment, a UV laser equipment and an eximerlaser equipment. The preferred diameter is preferably 100 to 200 μm.Among said machines, the carbon dioxide gas laser equipment, whichfeatures a high processing speed and a low-cost operation and, hence, ismost suited for industrial use, is the laser processor of choice for thepractice of the invention of the sixth group.

In Example 17, when 20 to 50% of the bottom of via holes 6060 isconnected lands 6036 a in the plated-through holes 6036, the sufficientelectrical connection thereof can be obtained.

As to the multilayer printed circuit board according to Example 17, thelower via holes 6060 were formed on the plated-through holes 6036 andthe upper via holes 6160 were formed on the lower via holes 6060, sothat the plated-through holes 6036 and the upper via holes 6160 weredeposited straight as a result the translation rate of an IC chip 6090was improved

EXAMPLE 18

The process for the multilayer printed circuit board according toExample 18 is now described with reference to FIG. 47 (A).

As to the multilayer printed circuit board according to Example 16 or17, filled via structure was used for via holes 6060. On the other hand,as to the multilayer printed circuit board according to Example 18, thesurface of via holes 6060 was flattened to form the upper via holes 6160by leaving concaved areas 6056 a in the lower via holes 6060 and fillingsaid concaved areas 6056 a with the conductive pastes 6021.

As the conductive pastes, there can be used silver, there can be used aconductive paste which comprises at least one metal particle selectedfrom the group consisting of copper, gold, nickel, solder. As the metalparticle, a metal particle the surface of which is coated with adifferent kind of metal. For example, the metal particle of copper whosesurface is coated with a noble metal selected from gold and silver maybe used.

As the conductive pastes, there can be preferably used organicconductive pastes which contain metal particles, and thermosetting resinsuch as epoxy resin and polyphenylenesulfide (PPS) resin are added.

EXAMPLE 19

As to the multilayer printed circuit board according to Example 19 isnow described with reference to FIG. 47 (B).

As to the multilayer printed circuit board according to Example 18,concaved areas 6056 a in the lower via holes 6060 were filled with theconductive pastes 6021. On the other hand, as to the multilayer printedcircuit board according to Example 19, the surface of via holes 6060 wasflattened to form the upper via holes 6160 by filling said concavedareas 6056 a in the lower via holes 6060 with the resin 6121. Therefor,the multilayer printed circuit board according to Example 18 or 19 wasproduced more easily than that according to Example 16 or 17.

EXAMPLE 20

As to the multilayer printed circuit board according to Example 20 isnow described with reference to FIG. 48.

As to the multilayer printed circuit board according to Example 18 or19, concaved areas 6056 a in the lower via holes 6060 were filled withthe conductive pastes 6021 or resin 6121. On the other hand, as to themultilayer printed circuit board according to Example 20, the upper viaholes 6160 were formed without filling said concaved areas 6056 a in thelower via holes 6060. Therefor, the multilayer printed circuit boardaccording to Example 20 were produced more easily.

EXAMPLE 21

As to the multilayer printed circuit board according to Example 21 isnow described with reference to FIG. 49.

As to the multilayer printed circuit board according to Example 16,solder bumps 6076U, 6076D were disposed at the position a little farfrom the plated-through holes 6036. On the other hand, as to themultilayer printed circuit board according to Example 21, solder bumps6076U, 6076D were disposed immediately over the upper via holes 6160.Therefor, as to the multilayer printed circuit board according toExample 21, the lower-layer via holes 6060 were disposed immediatelyover plated-through holes 6036, upper-layer via holes 6160 were disposedimmediately over said lower-layer via holes 6060, and solder bumps6076U, 6076D were disposed immediately over the plated-through hole6036, therefore the plated-through hole 6036, lower-layer via hole 6060,upper-layer via hole 6160 and solder bumps 6076U, 6076D can be lined upin good registration so that the wiring length can be reduced toincrease the transmission speed of signals.

EXAMPLE 22

As to the multilayer printed circuit board according to Example 22 isnow described with reference to FIG. 50.

As to the multilayer printed circuit board according to Example 17,solder bumps 6076U, 6076D were disposed at the position a little farfrom the plated-through holes 6036. On the other hand, as to themultilayer printed circuit board according to Example 22, solder bumps6076U, 6076D were disposed immediately over the upper via holes 6160.Therefor, the multilayer printed circuit board according to Example 22had an advantage that the plated-through hole 6036, lower-layer via hole6060, upper-layer via hole 6160 and solder bumps 6076U, 6076D can belined up in good registration so that the wiring length can be reducedto increase the transmission speed of signals, and a large amount ofpower can be obtained instantaneously form the power layer.

In Example 22, the multilayer printed circuit board having two layers onone side is shown, but it is obvious without saying that the multilayerprinted circuit board having not less than three layers on one side maybe available.

INDUSTRIAL APPLICABILITY

Thus, in accordance with the constant-voltage pulse plating process usedin the first group of inventions, conductor circuit and via holes ofgood crystallinity and uniform deposition can be constructed on asubstrate and high-density wiring and highly reliable conductorconnections can be realized without annealing.

Moreover, the constant-voltage pulse plating process used in the firstgroup of inventions can be easily carried out using an inexpensive powersupply, e.g. a direct current source, by repeating application andinterruption of a voltage alternately through manipulation of an ON-OFFswitch. Thus, unlike the PR plating process requiring an expensive powersource, this process makes it possible to construct an electroplatedmetal layer of excellent crystallinity and uniform deposition on thesubstrate surface as well as in the openings for via holes, thus beingof great industrial advantage.

Furthermore, with the electroless plating solutions used in the firstand second inventions belonging to the second group, which containtartaric acid or its salt, the amount of hydrogen uptake in the platedmetal layer is so small that the residual stress in the plated metalfilm is decreased, with the result that the risk for peeling of the filmand of layers is low. Moreover, since the deposition rate can be reducedas compared with the prior art, a plated metal film of sufficientthickness can be formed even in fine via-hole openings. In addition, theplated metal film can be thoroughly removed by etching.

The printed circuit boards according to the fifth through seventhinventions belonging to the second group are highly reliable becausesaid electroless plating solution containing tartaric acid or a saltthereof yields an electroless plated metal film of good adhesion andhigh peel resistance on a roughened resin insulating layer as well aswithin via holes in a sufficient thickness.

The printed circuit board according to the eighth invention amonginventions of the second group is highly reliable because theelectroless plating solution containing tartaric acid, copper ion andnickel or other ion yields a plated metal film of high hardness and goodadhesion on a roughened resin insulating layer.

In the invention of the third group, the copper foil is reduced inthickness in advance so that a fine circuit pattern can be implemented.Moreover, because the thickness of the conductor circuit on the coreboard is not much different from the thickness of the conductor layer onthe interlayer resin insulating layer, an impedance alignment can beeasily obtained between said conductor circuit on the core board andconductor layer on the interlayer resin insulating layer, thuscontributing to an improved high-frequency characteristic of the printedcircuit board.

In addition, the surface of the interlayer resin insulating layer can beflattened without filling the inter-conductor gaps with a resin.

In accordance with the invention belonging to the fourth group, completefilling of via-hole openings and formation of conductor circuit can besimultaneously implemented without using an expensive equipment.

Moreover, since the via holes in the multilayer printed circuit boardcan be filled up by plating, the interlayer resin insulating layer canbe flat and smooth and the stacked via can also be constructed.

In accordance with the invention belonging to the fifth group, the landconfiguration of the plated-through hole can be true-round so that thedensity of plated-through hole wirings in a multilayer core board isimproved. Therefore, the buildup circuit stratum on the face side of acore board and the buildup stratum on the reverse side can beconsolidated in the same pace so that the number of layers constitutingthe top stratum and that of layers constituting the bottom stratum canbe equalized and hence the necessary number of layers can be minimized.Moreover, since via holes can be disposed in registration, the wiringlength within the printed circuit board can be decreased.

In the invention belonging to the sixth group, wherein lower-layer viaholes are disposed immediately over plated-through holes and upper-layervia holes are disposed immediately over said lower-layer via holes, theplated-through hole, lower-layer via hole and upper-layer via hole canbe lined up in good registration so that the wiring length can bereduced to increase the transmission speed of IC chip signals.

1. An electroplating process of electroplating an electricallyconductive substrate comprising: electroplating intermittently to apredetermined plating thickness using said substrate surface as acathode and a plating metal as an anode at a constant voltage betweensaid anode and said cathode by repeating application of a voltagebetween a cathode and an anode and interruption of said applicationalternately, wherein a voltage time/interruption time ratio is 0.1 to1.0, a voltage time is not longer than 10 seconds, and an interruptiontime is not less than 1×10⁻¹² seconds.